Trinseo PLC TSEOQ US Equity☆

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

The following discussion summarizes the significant factors affecting the operating results, financial condition, liquidity and cash flows of our Company as of and for the periods presented below. The following discussion and analysis should be read in conjunction with the audited consolidated financial statements and the accompanying notes thereto, included elsewhere within this Annual Report. The statements in this discussion regarding industry outlook, our expectations regarding our future performance, liquidity and capital resources and all other non-historical statements in this discussion are forward-looking statements and are based on the beliefs of our management, as well as assumptions made by, and information currently available to, our management and are made as of the date of this Annual Report. See “Cautionary Note Regarding Forward-Looking Statements.” Actual results could differ materially from those discussed in or implied by forward-looking statements as a result of various factors, including those discussed below and elsewhere within this Annual Report, particularly in Item 1A—“Risk Factors.” Definitions of capitalized terms not defined herein appear in the notes to our consolidated financial statements.

2023 Highlights

For the year ended December 31, 2023, we had net loss from continuing operations of $701.3 million, inclusive of a non-cash goodwill impairment charge of $349.0 million and a non-cash after-tax charge related to an increase in valuation allowances on deferred tax assets of $163.7 million in certain subsidiaries, as discussed below, and Adjusted EBITDA of $154.3 million. These impairment charges, equal to the full carrying value of the Engineered Materials reporting unit’s associated goodwill during the second quarter of 2023, do not affect the Company’s cash position and the Company remains encouraged by the businesses’ expected synergies and strategic value as it continues to evolve as a specialty material and sustainable solutions provider. Our year-to-date results were significantly impacted by continued persistent underlying demand weakness experienced across all reporting segments, especially in building & construction and consumer durables applications. However, the impact to our operating performance was mitigated by lower costs, commercial actions and the asset restructuring initiatives that were announced in the fourth quarter of 2022 and the second half of 2023.

Amid these uncertain market conditions, the Company implemented liquidity-focused actions, including reduced capital spending, operating expenses and working capital, generating a $47.4 million year-over-year increase in our cash balance. Further, there are no maintenance covenants on our debt agreements and no significant debt maturing until September 2025. Refer to the discussion below for further information and refer to “Non-GAAP Performance Measures” for discussion of our use of non-GAAP measures in evaluating our performance and a reconciliation of these measures. Refer to “Capital Resources and Liquidity” for further information. Highlights for the year are described below.

New Financing Arrangements

On September 8, 2023, the Company entered into $1,077.3 million in term loan borrowings (“2028 Refinance Term Loans”) under a separate senior secured credit facility. The net proceeds from the 2028 Refinance Term Loans were used to repay in full the outstanding principal amount of, and all accrued and unpaid interest on, the senior secured Term Loan B facility maturing in September 2024 (the “2024 Term Loan B”) and redeemed $385.0 million of the Company’s $500.0 million aggregate principal amount of 5.375% Notes due 2025 (the “2025 Senior Notes”). Refer to Note 17 in the consolidated financial statements for further details on these new financing arrangements.

41

Table of Contents

Asset Optimization and Corporate Restructuring

In response to the challenging macroeconomic conditions noted above, during the second half of 2023, Trinseo approved asset restructuring and corporate restructuring initiatives to improve its economic position and operating flexibility, reduce its exposure to cyclical commodity markets and reduce certain general and administrative costs. These actions consisted of the following:

● Closure of its PMMA extruded sheet production line at its Rho, Italy plant,

Sale of Matamoros, Mexico Manufacturing Facility

In April 2023, the Company entered into an agreement to sell its land, buildings and equipment at its PMMA sheet manufacturing facility in Matamoros, Mexico for a cash consideration of approximately $19.0 million, which was received in May 2023 when the transaction closed. The sale resulted in a pre-tax gain of $14.4 million recognized in the second quarter of 2023. This site was part of the previously-announced asset restructuring plan approved in the fourth quarter of 2022 to consolidate our sheet manufacturing business and optimize our resources.

Bristol Spill

On March 24, 2023, due to equipment failure at the Bristol, Pennsylvania facility, operated by our wholly-owned subsidiary, Altuglas LLC, an accidental release of a latex emulsion product occurred, which ultimately flowed into a local waterway (the “Bristol Spill”). We reported the event and cooperated closely with local, state, and federal authorities on the response activities. Water sampling conducted by the authorities did not detect site-related material in the waterway. The safety of our employees, our communities and our environment are a top priority, and we are committed to operate safely and without disturbance to our community. Refer to Note 20 in our consolidated financial statements for additional information related to this matter.

​

42

Table of Contents

Results of Operations

Results of Operations for the Years Ended December 31, 2023, 2022, and 2021

The table below sets forth our historical results of operations, and these results as a percentage of net sales for the periods indicated. Refer to the Company’s Form 10-K filed on February 27, 2023 for explanations of our results of operations for 2022 in comparison to 2021.

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ ​ Year Ended ​

​ ​ ​ December 31, ​

Impairment and other charges ​ ​ ​ 349.5 ​ 10 % ​ ​ 339.6 ​ 7 % ​ ​ 6.8 ​ — %

Acquisition purchase price hedge loss ​ ​ — ​ — % ​ — ​ — % ​ 22.0 ​ — %

Other expense (income), net ​ ​ (17.2) ​ — % ​ (6.4) ​ — % ​ 9.0 ​ — %

2023 vs. 2022

Net Sales

Of the 26% decrease in net sales, 14% was due to lower selling prices resulting mainly from the pass through of lower raw material costs. Lower sales volume resulted in a 13% decrease due to continued customer destocking and underlying persistent market demand weakness stemming from an uncertain economic and geopolitical macroenvironment, particularly in applications supporting building & construction and consumer durables.

Cost of Sales

The 25% decrease in cost of sales was primarily attributable to a 14% decrease in raw material costs and an 11% decrease due to lower sales volumes.

Gross Profit

The decrease in gross profit of 48% was primarily attributable to lower sales volume as discussed above as well as lower margins from weaker market conditions including low demand and available supply. Margins were also pressured by unfavorable impacts from natural gas hedges. See the segment discussion below for further information.

43

Table of Contents

Selling, General and Administrative Expenses

The $88.5 million, or 22%, decrease in SG&A was primarily due to a decrease of $58.9 million in costs associated with the Company’s strategic initiatives, including the exploration of a potential divestiture of our styrenics business, a $5.6 million decrease in acquisition transaction and integration costs, and a $24.2 million decrease in restructuring costs driven by the asset optimization and corporate restructuring plan approved in the third quarter of 2023 and the asset restructuring plan approved in the fourth quarter of 2022.

Equity in Earnings of Unconsolidated Affiliates

The decrease in equity earnings of $40.1 million was due mainly to lower styrene and polystyrene margins from weaker market conditions.

Impairment and other charges

During the year ended December 31, 2023, the Company recorded a non-cash goodwill impairment charge of $349.0 million related to the Engineered Materials reporting unit, as described within Note 15 in the consolidated financial statements. The Company also recorded impairment charges of $0.5 million and $6.3 million related to the Boehlen styrene monomer assets during the years ended December 31, 2023 and 2022, respectively, as described within Note 19 in the consolidated financial statements.

Interest Expense, Net

The increase in interest expense, net of $75.5 million, or 67%, was primarily attributable to the year-over-year increase in market interest rates on our variable rate debt. Refer to Note 17 in the consolidated financial statements for further information.

(Gain) Loss on Extinguishment of Long-Term Debt

Loss on extinguishment of long-term debt was $6.3 million for the year ended December 31, 2023, which related to the Company’s debt refinancing during the third quarter of 2023. This amount was primarily comprised of the write-off of unamortized deferred financing costs and unamortized original issue discount related to the 2024 Term Loan B as well as the write-off of unamortized deferred financing costs related to the 2025 Senior Notes.

A $0.8 million gain on extinguishment of debt was recorded for the year ended December 31, 2022, in relation to the repurchase of $3.0 million of the 2029 Senior Notes in the open market.

Other Expense (Income), Net

Other income, net for the year ended December 31, 2023 was $17.2 million. Other income, net was comprised of foreign exchange transaction gains of $9.1 million, which included $16.7 million of foreign exchange transaction gains primarily from the remeasurement of our euro denominated payables due to the relative changes in rates between the U.S. dollar and the euro during the period, partially offset by $7.6 million of losses from our foreign exchange forward contracts.

Other income, net for the year ended December 31, 2022 was $7.2 million. Other income, net was comprised of foreign exchange transaction gains of $8.0 million, which included $41.0 million of foreign exchange transaction losses primarily from the remeasurement of our euro denominated payables due to the relative changes in rates between the U.S. dollar and the euro during the period, more than offset by $49.0 million of gains from our foreign exchange forward contracts.

Provision for (Benefit from) Income Taxes

Provision for (benefit from) income taxes was $68.4 million and $(41.6) million for the years ended December 31, 2023 and 2022, respectively, which resulted in an effective tax rate of (11)% and 9%, respectively. The increase in provision for income taxes in 2023 was primarily due to the increase in valuation allowance adjustments of $163.7 million, predominantly in the United States and Switzerland. This was partially offset by the $163.2 million decrease in

44

Table of Contents

income from continuing operations before income taxes, as well as the revaluation of the Company’s net deferred tax assets during the second quarter of 2022, which resulted in a one-time deferred tax expense of $15.3 million.

Net Income (Loss) from Discontinued Operations, Net of Income Taxes

There was no net income from discontinued operations, net of income taxes during the year ended December 31, 2023. Net income (loss) from discontinued operations, net of income taxes during the year ended December 31, 2022 was $(2.9) million and was related to the results and sale of our Synthetic Rubber business. Refer to Note 5 in the consolidated financial statements for further information.

Selected Segment Information

The Company’s reportable segments are as follows: Engineered Materials, Latex Binders, Plastics Solutions, Polystyrene, Feedstocks, and Americas Styrenics. Refer to Item 1—Business for a description of our segments, including a detailed overview, products and end uses, and competition and customers.

The following sections present net sales, Adjusted EBITDA, and Adjusted EBITDA margin by segment for the years ended December 31, 2023, 2022, and 2021. Inter-segment sales have been eliminated. Refer to Note 24 in the consolidated financial statements for a detailed definition of Adjusted EBITDA and a reconciliation of income from continuing operations before income taxes to segment Adjusted EBITDA. Refer to the Company’s Form 10-K filed on February 27, 2023 for explanations of our segment results for 2022 in comparison to 2021.

Engineered Materials Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

Adjusted EBITDA ​ $ 4.9 ​ ​ $ 71.6 ​ ​ $ 94.8 ​ ​ (93) % (24) % ​

Adjusted EBITDA margin ​ 1 % ​ 7 % ​ 13 % ​ ​ ​ ​ ​ ​

2023 vs. 2022

The 24% decrease in net sales was primarily attributable to lower pricing, primarily from the pass through of lower raw materials and energy costs which contributed to a 14% decrease year-over-year. Lower sales volumes from weak underlying demand and continued customer destocking, primarily in building & construction, consumer electronics, and wellness applications contributed to an 11% decrease year-over-year.

Adjusted EBITDA decreased $66.7 million, or 93%, year-over-year primarily due to lower margins which decreased by $61.1 million or 85% year-over-year, as well as a decrease of $14.3 million, or 20%, due to lower sales volumes as described above. These were partially offset by lower fixed costs of $7.1 million, or 10%, primarily as the result of restructuring activities undertaken in late 2022 and 2023.

​

​

45

Table of Contents

Latex Binders Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

Adjusted EBITDA margin ​ 10 % ​ 9 % ​ 9 % ​ ​ ​ ​ ​ ​

2023 vs. 2022

The 25% decrease in net sales was primarily due to a 12% decrease in pricing from the pass through of lower raw material costs, and a 14% decrease due to lower sales volumes across most applications from customer destocking and impacts from geopolitical uncertainty.

The $17.5 million, or 16%, decrease in Adjusted EBITDA was primarily due to a decrease of $40.2 million, or 36%, from lower sales volume. These decreases were partially offset by a $25.9 million, or 23%, increase attributable to higher margins primarily due to pricing initiatives.

Plastics Solutions Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

Adjusted EBITDA ​ $ 89.4 ​ ​ $ 91.0 ​ ​ $ 314.2 ​ ​ (2) % (71) % ​

Adjusted EBITDA margin ​ 9 % ​ 7 % ​ 21 % ​ ​ ​ ​ ​ ​

2023 vs. 2022

Of the 22% decrease in net sales, 10% was due to lower sales volumes, which were primarily impacted by a decrease in polycarbonate from the announced shutdown of one production line as well as in copolymers in building & construction, industrial, and consumer durables applications from customer destocking and a weaker macroeconomic environment. The volume decrease was partially offset by higher volumes to automotive applications. Also contributing to the overall decrease was a 12% decrease from lower pricing due to the pass through of lower raw material costs.

The $2.0 million, or 2%, decrease in Adjusted EBITDA was primarily due to lower sales volume of $8.6 million, or 9%. These decreases were partially offset by lower fixed costs which contributed a $2.8 million, or 3%, increase in Adjusted EBITDA. Margins also improved 2% versus prior year leading to a $1.5 million increase in Adjusted EBITDA.

​

46

Table of Contents

Polystyrene Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

Adjusted EBITDA margin ​ 4 % ​ 9 % ​ 16 % ​ ​ ​ ​ ​ ​

2023 vs. 2022

Net sales decreased by 32% year-over-year. Lower sales volumes, primarily due to customer destocking and a weak overall demand environment amid falling raw material prices, led to a 16% decrease in net sales from prior year. Also contributing to the overall decrease was a 17% decrease from lower pricing, primarily from the pass through of lower styrene costs.

The $66.0 million, or 66%, decrease in Adjusted EBITDA was due to a decrease of $33.3 million, or 34%, from lower margins and a decrease of $27.5 million, or 28%, due to lower volumes. Weaker demand, including in building & construction and appliance applications, contracted margins and led to lower volumes.Also contributing to the overall decrease was a $5.3 million, or 5%, decrease from higher fixed costs.

Feedstocks Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

Adjusted EBITDA margin ​ (25) % ​ (30) % ​ 12 % ​ ​ ​ ​ ​ ​

2023 vs. 2022

Net sales decreased 33% year-over-year. Lower styrene-related sales volume resulted in a 10% decrease along with a 24% decrease due to lower styrene prices.

The increase of $34.4 million in Adjusted EBITDA was primarily attributed to an increase of $18.0 million, or 24%, from lower fixed costs mainly due to the December 2022 Boehlen, Germany styrene plant closure. Also contributing to the overall increase was a $17.2 million, or 23%, increase from higher styrene margins.

Americas Styrenics Segment

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​ ​ ​ ​ ​

​ ​ December 31, ​ ​ Percentage Change ​ ​

*The results of this segment are comprised entirely of earnings from Americas Styrenics, our equity method investment. As such, Adjusted EBITDA related to this segment is included within “Equity in earnings of unconsolidated affiliates” in the consolidated statements of operations.

2023 vs. 2022

The decrease in Adjusted EBITDA was mainly due to lower styrene margins compared to the high levels in the prior year.

47

Table of Contents

Outlook

We expect a constrained demand environment in 2024 similar to 2023, however, sequential headwinds in the second half of 2024, such as negative net timing impacts, are not expected to repeat and we expect the benefit of our restructuring actions take effect.

Despite the economic environment, the Company maintains access to capital resources through continued focus on liquidity improvement actions. Also, we are seeing the benefit of our announced asset restructuring initiatives and anticipate these actions will result in meaningful cost savings in 2024. We believe these actions will better position us to achieve higher growth, higher margin, and lower volatility as demand normalizes.

Non-GAAP Performance Measures

We present Adjusted EBITDA as a non-GAAP financial performance measure, which we define as income from continuing operations before interest expense, net; provision for income taxes; depreciation and amortization expense; loss on extinguishment of long-term debt; asset impairment charges; gains or losses on the dispositions of businesses and assets; restructuring charges; acquisition related costs and other items. In doing so, we are providing management, investors, and credit rating agencies with an indicator of our ongoing performance and business trends, removing the impact of transactions and events that we would not consider a part of our core operations.

There are limitations to using the financial performance measures such as Adjusted EBITDA. This performance measure is not intended to represent net income or other measures of financial performance. As such, it should not be used as an alternative to net income as an indicator of operating performance. Other companies in our industry may define Adjusted EBITDA differently than we do. As a result, it may be difficult to use this or similarly-named financial measures that other companies may use, to compare the performance of those companies to our performance. We compensate for these limitations by providing a reconciliation of this performance measure to our net income, which is determined in accordance with accounting principles generally accepted in the United States of America (“GAAP”).

Adjusted EBITDA is calculated as follows for the years ended December 31, 2023, 2022, and 2021. For discussion related to 2021 activity, refer to the Company’s Form 10-K filed on February 27, 2023.

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​

​ ​ December 31,

Net income (loss) from discontinued operations ​ ​ — ​ ​ (2.9) ​ ​ 160.4 ​

Net income (loss) from continuing operations ​ ​ (701.3) ​ ​ (428.0) ​ ​ 279.6 ​

Provision for (benefit from) income taxes ​ 68.4 ​ (41.6) ​ 70.9 ​

Restructuring and other charges(c) ​ ​ 31.4 ​ ​ 15.9 ​ 9.0 ​

Acquisition purchase price hedge loss (e) ​ ​ — ​ ​ — ​ ​ 22.0 ​

Asset impairment charges or write-offs(f) ​ ​ 2.7 ​ ​ 6.3 ​ ​ 6.8 ​

European Commission request for information(g) ​ ​ — ​ ​ 36.2 ​ ​ — ​

Goodwill impairment charges(h) ​ ​ 349.0 ​ ​ 297.1 ​ ​ — ​

48

Table of Contents

Note that the accelerated depreciation charges incurred as part of both the Company’s asset restructuring plan and corporate restructuring program are included within the “Depreciation and amortization” caption above, and therefore are not included as a separate adjustment within this caption.

Liquidity and Capital Resources

Capital Resources, Indebtedness and Liquidity

We require cash principally for day-to-day operations, to finance capital investments and other initiatives, to purchase materials, to service our outstanding indebtedness, and to fund the return of capital to shareholders via dividend payments and ordinary share repurchases, when deemed appropriate. Our sources of liquidity include cash on hand, cash flow from continuing operations, and amounts available under the Senior Credit Facility and the Accounts Receivable Securitization Facility (discussed further below).

The 2028 Refinance Credit Agreement requires the Company to comply with customary affirmative, negative and financial covenants, and contains events of default including (i) relating to a change of control or (ii) failure to maintain at least $100.0 million of Liquidity at the end of any calendar month, and (iii) a cross default to the Credit Agreement. If an event of default occurs, the Term Lenders will be entitled to take various actions, including the acceleration of amounts due under the 2028 Refinance Term Loans. Liquidity is defined under the 2028 Refinance Credit Agreement as a combination of cash and cash equivalents held at certain of the Company’s restricted subsidiaries as well as the funds available for borrowing under both the 2026 Revolving Facility and the Accounts Receivable Securitization Facility, subject to certain restrictions outlined in the 2028 Refinance Credit Agreement. As of December 31, 2023, the Company was in compliance with all debt covenant requirements under the 2028 Refinance Credit Agreement and the Credit Agreement.

As of December 31, 2023, the Company had Liquidity of $471.0 million, comprised of $259.1 million of cash and cash equivalents and approximately $211.9 million of funds available for borrowing under both the 2026 Revolving Facility and the Accounts Receivable Securitization Facility, $98.4 million and $113.5 million respectively. As of

49

Table of Contents

December 31, 2023 and 2022, we had $2,344.6 million and $2,353.7 million, respectively, in outstanding indebtedness and $521.5 million and $701.3 million, respectively, in working capital (calculated as current assets from continuing operations less current liabilities from continuing operations). In addition, as of December 31, 2023 and 2022, we had $161.4 million and $168.7 million, respectively, of foreign cash and cash equivalents on our consolidated balance sheets, outside of our country of domicile, which was Ireland as of December 31, 2023 and 2022, all of which is readily convertible into other foreign currencies, including the U.S. dollar. Our intention is not to permanently reinvest our foreign cash and cash equivalents. Accordingly, we record deferred income tax liabilities related to the unremitted earnings of our subsidiaries. For a detailed description of the Company’s debt structure, borrowing rates, and expected future payment obligations, refer to Note 17 in the consolidated financial statements.

The following table outlines our outstanding indebtedness as of December 31, 2023 and 2022 and the associated interest expense, including amortization of deferred financing fees and issuance discounts. Effective interest rates for the borrowings included in the table below exclude the impact of deferred financing fee amortization, certain other fees charged to interest expense (such as fees for unused commitment fees during the period), and the impacts of derivatives designated as hedging instruments.

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ As of and for the Year Ended ​ As of and for the Year Ended

​ ​ ​ ​ Effective ​ ​ ​ ​ ​ Effective ​ ​

​ ​ ​ ​ Interest ​ Interest ​ ​ ​ Interest ​ Interest

($ in millions) Balance Rate Expense Balance ​ Rate Expense

Senior Credit Facility ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

2026 Revolving Facility ​ ​ — ​ — % ​ 2.3 ​ ​ — ​ — % ​ 1.8 ​

Accounts Receivable Securitization Facility ​ — ​ — % 1.3 ​ — ​ — % 1.4 ​

Other indebtedness ​ 7.2 ​ — % 0.4 ​ 7.4 ​ 5.1 % 0.1 ​

Our Senior Credit Facility includes the 2026 Revolving Facility, which matures in May 2026 and has a borrowing capacity of $375.0 million. The 2026 Revolving Facility contains a springing covenant which applies when 30% or more is drawn from the facility and would require the Company to meet a first lien net leverage ratio not to exceed 3.50x at the end of each financial quarter. As of December 31, 2023 the first lien net leverage ratio (as defined in our secured credit agreement) was 5.43x. As of December 31, 2023, the Company had $98.4 million of funds available for borrowing (net of $14.1 million outstanding letters of credit) under the 2026 Revolving Facility. Further, as of December 31, 2023, the Company is required to pay a quarterly commitment fee in respect of any unused commitments under the 2026 Revolving Facility equal to 0.375% per annum.

On September 8, 2023, the Company entered into a Credit Agreement (the “2028 Refinance Credit Agreement”) which provides for a senior secured term loan facility of $1,077.3 million maturing in May 2028 (the “2028 Refinance Term Loans”). The 2028 Refinance Term Loans bear interest at a rate per annum equal to Term SOFR (as defined in the 2028 Refinance Credit Agreement) plus 8.50%, subject to a 3.00% SOFR floor, and was issued at a 3.0% original issue discount. Further, the 2028 Refinance Term Loans require scheduled quarterly payments, commencing on January 2, 2024, in amounts equal to 0.25% of the original principal amount of the 2028 Refinance Term Loans, with the balance to be paid at maturity.

Also included in our Senior Credit Facility is our 2028 Term Loan B (with original principal of $750.0 million, maturing in May 2028), which requires scheduled quarterly payments in amounts equal to 0.25% of the original principal. The stated interest rate on our 2028 Term Loan B is SOFR plus 2.50% (subject to a 0.00% SOFR floor). The Company fully repaid the 2024 Term Loan B during the year ended December 31, 2023, while making $7.5 million of net principal payments on the 2028 Term Loan B, with an additional $18.3 million of scheduled future payments classified within current debt on the Company’s consolidated balance sheet as of December 31, 2023 related to both the 2028 Refinance Term Loans and the 2028 Term Loan B.

50

Table of Contents

Our 2025 Senior Notes issued under the indenture executed in 2017 include $115.0 million aggregate principal amount of 5.375% senior notes that mature on September 1, 2025. Interest on the 2025 Senior Notes is payable semi-annually on May 3 and November 3 of each year. These Notes may be redeemed prior to their maturity at the option of the Company under certain circumstances at specific redemption prices. Refer to Note 17 in the consolidated financial statements for further information.

Our 2029 Senior Notes (with original principal of $500.0 million), as issued under the indenture executed in 2021, include $447.0 million aggregate principal amount of 5.125% senior notes that mature on April 1, 2029. Interest on the 2029 Senior Notes is payable semi-annually on February 15 and August 15 of each year, which commenced on August 15, 2021. These Notes may be redeemed prior to their maturity at the option of the Company under certain circumstances at specific redemption prices. Refer to Note 17 in the consolidated financial statements for further information.

We also continue to maintain our Accounts Receivable Securitization Facility, which matures in November 2024 and has an outstanding borrowing capacity of $150.0 million. As of December 31, 2023, there were no amounts outstanding under this facility and the Company had approximately $113.5 million of accounts receivable available to support this facility, based on the pool of eligible accounts receivable.Refer to Note 17 in the consolidated financial statements for further information on the facility.

Our ability to raise additional financing and our borrowing costs may be impacted by short- and long-term debt ratings assigned by independent rating agencies, which are based, in significant part, on our performance as measured by certain credit metrics such as interest coverage and leverage ratios.

We and our subsidiaries, affiliates, or significant shareholders may from time to time seek to retire or purchase our outstanding debt through cash purchases in the open market, privately negotiated transactions, exchange transactions or otherwise. Such repurchases or exchanges, if any, will depend on prevailing market conditions, our liquidity requirements, contractual restrictions and other factors. The amounts involved may be material.

Trinseo Materials Operating S.C.A. and Trinseo Materials Finance, Inc. (the “Issuers” of our 2029 Senior Notes and 2025 Senior Notes and “Borrowers” under our Senior Credit Facility) are dependent upon the cash generation and receipt of distributions and dividends or other payments from our subsidiaries and joint venture in order to satisfy their debt obligations. There are no known significant restrictions by third parties on the ability of subsidiaries of the Company to disburse or dividend funds to the Issuers and the Borrowers in order to satisfy these obligations. However, as the Company’s subsidiaries are located in a variety of jurisdictions, the Company can give no assurances that our subsidiaries will not face transfer restrictions in the future due to regulatory or other reasons beyond our control.

The Senior Credit Facility and Indentures also limit the ability of the Borrowers and Issuers, respectively, to pay dividends or make other distributions to Trinseo PLC, which could then be used to make distributions to shareholders. During the year ended December 31, 2023, the Company declared total dividends of $0.17 per ordinary share, or $6.2 million, of which $0.9 million, inclusive of dividend equivalents, remains accrued as of December 31, 2023 and the majority of which was paid in January 2024. These dividends are well within the available capacity under the terms of the restrictive covenants contained in the Senior Credit Facility and Indentures. Further, significant additional capacity continues to be available under the terms of these covenants to support expected future dividends to shareholders, should the Company continue to declare them.

Despite the economic environment, the Company maintains access to capital resources through continued focus on liquidity improvement actions. The cash flows provided by operating activities was $148.7 million for the year ended December 31, 2023. Due to the expectation that operating conditions in the beginning of 2024 will be largely similar to 2023, the Company may exceed the first lien net leverage ratio in 2024, which would limit the availability of the 2026 Revolving Facility to 30% of the total capacity. However, we believe funds provided by operations, our existing cash and cash equivalent balances of $259.1 million, coupled with borrowings available under our 2026 Revolving Facility and our Accounts Receivable Securitization Facility totaling a minimum of $211.9 million, which reflects the potential borrowing limit imposed by the aforementioned springing covenant, will be adequate to meet all necessary operating and capital expenditures for at least the next 12 months under current operating conditions.

Further, we also believe that our financial resources will allow us to manage the anticipated impact of this challenging macroeconomic environment on our business operations for the foreseeable future, which could include lower demand, reductions in revenue or delays in payments from customers and other third parties. Our ability to generate cash from operations to pay our indebtedness and meet other liquidity needs is subject to certain risks described

51

Table of Contents

herein and under Item 1A – Risk Factors. As of December 31, 2023, we were in compliance with all the covenants and default provisions under our debt agreements. Refer to Note 17 in the consolidated financial statements for further information on the details of the covenant requirements.

We do not have any off-balance sheet financing arrangements that we believe are reasonably likely to have a material current or future effect on our financial condition, revenues or expenses, results of operations, liquidity, capital expenditures or capital resources.

Cash Flows

The table below summarizes our primary sources and uses of cash for the years ended December 31, 2023, 2022, and 2021. We have derived the summarized cash flow information from our audited financial statements. Refer to the Company’s Form 10-K filed on February 27, 2023 for discussion related to 2021.

​

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended

​ ​ December 31,

Net cash provided by (used in): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Operating activities - continuing operations ​ $ 148.7 ​ $ 46.4 ​ $ 456.0 ​

Operating activities - discontinued operations ​ ​ — ​ ​ (2.9) ​ ​ (3.3) ​

Investing activities - continuing operations ​ (31.7) ​ (163.2) ​ (1,936.2) ​

Investing activities - discontinued operations ​ ​ — ​ ​ (0.8) ​ ​ 396.5 ​

Effect of exchange rates on cash ​ (1.6) ​ (7.1) ​ (4.4) ​

Operating Activities

Net cash provided by operating activities from continuing operations during the year ended December 31, 2023 totaled $148.7 million, inclusive of dividends received from Americas Styrenics of $65.0 million. Although operating results continued to be challenged by customer destocking and macroeconomic conditions, which resulted in reduced customer demand and negative earnings, there was a significant increase in cash performance during the year primarily as a result of targeted inventory control actions and cash improvement initiatives. Further, there was an increase in interest payments driven by the 2029 Senior Notes and the 2028 Term Loan B, both of which were outstanding for the full year, as well as the impact of the rising interest rates on our variable rate debt. Tax payments also increased, driven by higher earnings before income taxes in the prior year. Net cash used in operating activities from discontinued operations during the year ended December 31, 2023 was not significant.

Net cash provided by operating activities from continuing operations during the year ended December 31, 2022 totaled $46.4 million, inclusive of dividends received from Americas Styrenics of $95.0 million. Although operating results were challenged by macroeconomic conditions resulting in reduced customer demand, higher raw material and utility costs and negative earnings, there was a slight working capital build during the year. The rapid and significant increase in raw material prices, along with the historically high energy prices led to a significant working capital build in the first half of 2022. This build was largely offset with the working capital release in the second half of the year, primarily attributable to a steep decline in many raw material prices from the historically high prices seen in the second quarter, inventory control actions, and sequentially lower sales. Operating activities also included a one-time payment of $33.8 million related to the settlement of the European Commission request for information as described in Note 20 in the consolidated financial statements. Further, there was an increase in interest payments driven by the 2029 Senior Notes and the 2028 Term Loan B, both of which were outstanding for the full year, as well as the impact of the rising interest rates on our variable rate debt. Tax payments also increased, driven by higher earnings before income taxes in the prior year. Net cash used in operating activities from discontinued operations during the year ended December 31, 2022 totaled $2.9 million.

52

Table of Contents

Investing Activities

Net cash used in investing activities from continuing operations during the year ended December 31, 2023 totaled $31.7 million, which was primarily attributable to capital expenditures of $69.7 million offset by proceeds from the sale of business and other assets of $38.0 million. The Company has taken proactive measures to reduce and defer capital expenditures during the year as part of our liquidity improvement actions. Net cash used in investing activities from discontinued operations during the year ended December 31, 2023 was not significant.

Capital expenditures for 2024 are expected to be approximately $72.0 million, inclusive of spending for both compliance and maintenance costs, and growth initiatives, including material substitution applications as well as products containing recycled or bio-based materials.

Net cash used in investing activities from continuing operations during the year ended December 31, 2022 totaled $163.2 million, which was primarily attributable to net cash paid for asset or business acquisitions of $22.2 million (see Note 4 in the consolidated financial statements), and capital expenditures of $148.2 million, including cash spent for our ongoing enterprise resource planning system upgrade. Net cash used in investing activities from discontinued operations during the year ended December 31, 2022 totaled $0.8 million.

Financing Activities

Net cash used in financing activities during the year ended December 31, 2023 totaled $66.0 million. This activity was primarily due to $1,055.9 million in debt repayments, $23.4 million in deferred financing fees related to the issuance of the 2028 Refinance Term Loans, $17.9 million of dividends paid, and $10.5 million of net repayments of short-term borrowings. This activity was partially offset by $1,044.9 million in proceeds from the issuance of the 2028 Refinance Term Loans.

Net cash used in financing activities during the year ended December 31, 2022 totaled $233.7 million. This activity was primarily due to $151.9 million of payments related to the repurchase of ordinary shares, $47.5 million of dividend payments, and $17.5 million of net repayments of short-term borrowings. In addition, there was $16.6 million of repurchases and repayments long-term debt during the period, primarily related to our 2024 Term Loan B and 2028 Term Loan B obligations.

​

Free Cash Flow

We use Free Cash Flow as a non-GAAP measure to evaluate and discuss the Company’s liquidity position and results. Free Cash Flow is defined as cash from operating activities, less capital expenditures. We believe that Free Cash Flow provides an indicator of the Company’s ongoing ability to generate cash through core operations, as it excludes the cash impacts of various financing transactions as well as cash flows from business combinations that are not considered organic in nature. We also believe that Free Cash Flow provides management and investors with useful analytical indicator of our ability to service our indebtedness, pay dividends (when declared), and meet our ongoing cash obligations.

Free Cash Flow is not intended to represent cash flows from operations as defined by GAAP, and therefore, should not be used as an alternative for that measure. Other companies in our industry may define Free Cash Flow differently than we do. As a result, it may be difficult to use this or similarly-named financial measures that other companies may use, to compare the liquidity and cash generation of those companies to our own. We compensate for these limitations by providing a reconciliation to cash provided by operating activities, which is determined in accordance with GAAP.

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Year Ended ​

​ ​ December 31, ​

Cash provided by operating activities ​ $ 148.7 ​ $ 43.5 ​ $ 452.7 ​

Capital expenditures ​ ​ (69.7) ​ ​ (149.0) ​ ​ (123.5) ​

Refer to the discussion above for significant impacts to cash provided by operating activities for the years ended December 31, 2023 and 2022. Refer to the Company’s Form 10-K filed on February 27, 2023 for discussion related to 2021.

​

53

Table of Contents

Contractual Obligations and Commercial Commitments

The Company’s primary contractual obligations and commercial commitments consist of the payments for principal and interest on our outstanding long-term debt, raw material purchases, funding requirements under our pension and other postretirement benefits, lease commitments, and obligations under our SAR SSAs.

The Company has both fixed and variable-rate long-term debt arrangements, which have varying principal and interest payment requirements over their contractual terms. Refer to the table and section above as well as to Note 17 in the consolidated financial statements for more information on our debt arrangements. Additionally, refer to Item 7A—Quantitative and Qualitative Disclosures about Market Risk for discussion of our interest rate and foreign currency risks related to our debt and debt-related hedging arrangements.

The Company has certain raw material purchase contracts where we are required to purchase certain minimum volumes at the then prevailing market prices. As of December 31, 2023, the Company had $1,213.6 million of raw material purchase obligations, of which $531.6 million is due within the next twelve months. These commitments have remaining terms ranging from one to four years. Refer to Note 20 in the consolidated financial statements for more information on raw material purchase commitments. Additionally, refer to Item 1 – Business – Sources and Availability of Raw Materials for further description of the sources of our key raw materials.

The Company has various pension and other postretirement plans. The Company is required to make minimum contributions to certain of our funded pension plans and is also obligated to make benefit payments to employees for the unfunded pension plans and other postretirement plans. As of December 31, 2023, the Company’s estimated future benefit payments through 2033, reflecting expected future service, as appropriate, was $140.5 million, of which $9.9 million is due within the next twelve months. Refer to the section of our Critical Accounting Policies and Estimates entitled “Pension Plans and Postretirement Benefits” for more information on the factors impacting our pension and postretirement costs. Additionally, refer to Note 22 in the consolidated financial statements for more details on these employee benefit plans and the future payments expected to be made for them through 2033.

The Company has operating and finance leases for certain of its plant and warehouse sites, office spaces, rail cars, storage facilities, and equipment. The Company’s leases have remaining terms of one month through twelve years. As of December 31, 2023, the Company’s estimated minimum commitments related to our finance and operating lease obligations was $84.0 million, of which $19.3 million is due within the next twelve months. Refer to Note 21 in the consolidated financial statements for further information on our lease portfolio and future lease obligations.

As described in Item 1— Business— Our Relationship with Dow, the Company is party to SAR SSAs with Dow, which are agreements under which Dow provides certain site services to the Company at Dow-owned locations. Based on our current year known costs and assuming that we continue with the SAR SSAs with similar annualized costs going forward, we estimate our contractual obligations under these agreements to be approximately $89.8 million annually for 2024 through 2028, and a total of $896.7 million thereafter through June 2040. Refer to the aforementioned section of Item 1 for more information regarding these agreements, including details regarding the rights of the Company and Dow to terminate said agreements.

Derivative Instruments

The Company’s ongoing business operations expose it to various risks, including fluctuating foreign exchange rates, interest rate risk, and commodity price risk. To manage this risk, the Company periodically enters into derivative financial instruments, such as foreign exchange forward contracts, interest rate swap agreements, and commodity swap agreements. A summary of these derivative financial instrument programs is described below; however, refer to Note 18 of the consolidated financial statements for further information. The Company does not hold or enter into financial instruments for trading or speculative purposes.

Foreign Exchange Forward Contracts

Certain subsidiaries have assets and liabilities denominated in currencies other than their respective functional currencies, which creates foreign exchange risk. Our principal strategy in managing exposure to changes in foreign currency exchange rates is to naturally hedge the foreign currency-denominated liabilities on our consolidated balance sheets against corresponding assets of the same currency such that any changes in liabilities due to fluctuations in exchange rates are offset by changes in their corresponding foreign currency assets. In order to further reduce our

54

Table of Contents

exposure, the Company uses foreign exchange forward contracts to economically hedge the impact of the variability in exchange rates on our assets and liabilities denominated in certain foreign currencies. These derivative contracts are not designated for hedge accounting treatment.

Foreign Exchange Cash Flow Hedges

The Company also enters into forward contracts with the objective of managing the currency risk associated with forecasted U.S. dollar-denominated raw materials purchases by one of our subsidiaries whose functional currency is the euro. By entering into these forward contracts, which are designated as cash flow hedges, the Company buys a designated amount of U.S. dollars and sells euros at the prevailing market rate to mitigate the risk associated with the fluctuations in the euro-to-U.S. dollar foreign currency exchange rate.

Commodity Cash Flow Hedges & Commodity Economic Hedges

The Company purchases certain commodities, primarily natural gas, to operate facilities and generate heat and steam for various manufacturing processes, which are subject to price volatility. In order to manage the risk of price fluctuations associated with these commodity purchases, as deemed appropriate, the Company may enter into commodity swaps agreements or option contracts. Under these derivative contracts, the Company is effectively converting a portion of our natural gas costs into a fixed rate obligation to mitigate the risk of price fluctuations associated with the underlying commodity purchases. Certain of these commodity swaps are designated as cash flow hedges (“commodity cash flow hedges”), and the remaining commodity swaps are not designated for hedge accounting treatment (“commodity economic hedges”).

Interest Rate Swaps

The Company enters into interest rate swap agreements to manage our exposure to variability in interest payments associated with the Company’s variable rate debt. Under these interest rate swap agreements, which are designated as cash flow hedges, the Company is effectively converting a portion of our variable rate borrowings into a fixed rate obligation to mitigate the risk of variability in interest rates. The Company does not have any outstanding interest rate swap agreements as of December 31, 2023.

Net Investment Hedge

The Company had certain fixed-for-fixed cross currency swaps (“CCS”), swapping U.S. dollar principal and interest payments on our 2025 Senior Notes for euro-denominated payments, which were designated as a hedge of the Company’s net investment in certain European subsidiaries under the spot method through the original CCS agreement entered into on September 1, 2017 (“2017 CCS”). As such, changes in the fair value of the 2017 CCS that were included in the assessment of effectiveness (changes due to spot foreign exchange rates) were recorded as cumulative foreign currency translation within accumulated other comprehensive income or loss (“AOCI”), and will remain in AOCI until either the sale or substantially complete liquidation of the subsidiary. Additionally, the initial value of any component excluded from the assessment of effectiveness is recognized in income using a systematic and rational method over the life of the hedging instrument. Any difference between the change in the fair value of the excluded component and amounts recognized in income under that systematic and rational method is recognized in AOCI. The Company elected to amortize the initial excluded component value as a reduction of “Interest expense, net” in the consolidated statements of operations using the straight-line method over the remaining term of the 2017 CCS. Additionally, the Company recognizes the accrual of periodic USD and euro-denominated interest receipts and payments under the terms of CCS arrangements, including the 2017 CCS, within “Interest expense, net” in the consolidated statements of operations.

On February 26, 2020, the Company settled our 2017 CCS and replaced it with a new CCS arrangement (the “2020 CCS”) that carried substantially the same terms as the 2017 CCS and also is designated as a net investment hedge under the spot method. Upon settlement of the 2017 CCS, the Company realized net cash proceeds of $51.6 million. The remaining $13.8 million unamortized balance of the initial excluded component related to the 2017 CCS at the time of settlement is no longer being amortized following the settlement and will remain in AOCI until either the sale or substantially complete liquidation of the relevant subsidiaries. On April 7, 2022, the Company settled its existing 2020 CCS, which was set to mature in November 2022. Upon settlement of the 2020 CCS, the Company realized net cash proceeds of $1.9 million.

55

Table of Contents

Critical Accounting Policies and Estimates

Our discussion and analysis of results of operations and financial condition are based upon our financial statements, which have been prepared in accordance with GAAP. The preparation of these financial statements requires us to make estimates and judgments that affect the amounts reported. We base these estimates and judgments on historical experiences and assumptions believed to be reasonable under the circumstances. Actual results could vary from our estimates under different conditions. Our significant accounting policies, which may be affected by our estimates and assumptions, are more fully described in Note 2 in the consolidated financial statements. An accounting policy is deemed to be critical if it requires an accounting estimate to be made based on assumptions about matters that are highly uncertain at the time the estimate is made, and if different estimates that reasonably could have been used, or changes in the accounting estimates that are reasonably likely to occur periodically, could materially impact the financial statements. The following critical accounting policies reflect our most significant estimates and assumptions used in the preparation of the consolidated financial statements.

Valuation of Assets and Impairment Considerations

Valuation of Assets

Acquisitions that qualify as a business combination are accounted for using the purchase accounting method. Amounts paid for an acquisition are allocated to the assets acquired and liabilities assumed based on their fair value as of the date of acquisition. Goodwill is recorded as the difference between the fair value of the acquired assets and liabilities assumed (net assets acquired) and the purchase price. Goodwill is not amortized, but is reviewed for impairment annually as of October 1, or when events or changes in the business environment indicate that the carrying value of a reporting unit may exceed its fair value. Refer to the discussion below for further information on asset impairments.

Under the purchase accounting method, the Company completes valuation procedures for an acquisition, often with the assistance of third-party valuation specialists, to determine the fair value of the assets acquired and liabilities assumed. These valuation procedures require management to make assumptions and apply significant judgment to estimate the fair value of the assets acquired and liabilities assumed. If the estimates or assumptions used should significantly change, the resulting differences could materially affect the fair value of net assets.

Specifically, the calculation of the fair value of tangible assets, including property, plant and equipment, typically utilize the cost approach, which computes the cost to replace the asset, less accrued depreciation resulting from physical deterioration and functional and external obsolescence. The calculation of the fair value of identified intangible assets is determined using cash flow models following the income and cost approaches (or some combination thereof). Significant inputs include estimated future cash flows, discount rates, royalty rates, growth rates, sales projections, customer retention rates, and terminal values, all of which require significant management judgment. Definite-lived intangible assets, which are primarily comprised of customer relationships, developed technology, tradenames, and software, are amortized over their estimated useful lives using the straight-line method and are assessed for impairment whenever events or changes in circumstances indicate the carrying value of the asset may not be recoverable.

During the year ended December 31, 2022, the Company completed the Heathland Acquisition, which closed on January 3, 2022. Refer to Note 4 in the consolidated financial statements for further information on this transaction.

Impairment Considerations

As of December 31, 2023, net property, plant and equipment, net identifiable finite-lived intangible assets, and goodwill totaled $643.7 million, $693.9 million, and $63.8 million, respectively. Management makes estimates and assumptions in preparing the consolidated financial statements for which actual results will emerge over long periods of time. This includes the recoverability of long-lived assets employed in the business. These estimates and assumptions are closely monitored by management and periodically adjusted as circumstances warrant. For instance, expected asset lives may be shortened or impairment may be recorded based on a change in the expected use of the asset or performance of the related asset group.

We evaluate long-lived assets and identifiable finite-lived intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset grouping may not be recoverable. In the event the carrying value of the asset exceeds its undiscounted future cash flows and the carrying value is not considered

56

Table of Contents

recoverable, impairment may exist. An impairment loss, if any, is measured as the excess of the asset’s carrying value over its fair value, generally based on a discounted future cash flow method, independent appraisals, etc.

In connection with our strategy to focus efforts and increase investments in certain product offerings serving specific applications that are less cyclical and offer significantly higher growth and margin potential, and other management considerations, in March of 2020, the Company initiated a consultation process with the Economic Council and Works Councils of Trinseo Deutschland regarding the disposition of our styrene monomer assets in Boehlen, Germany. The Company’s assessments of these long-lived asset groups for impairment indicated that the carrying values of the asset groups at each location were not recoverable when compared to the expected undiscounted future cash flows from the operation and potential disposition of these assets. The fair value of the depreciable assets at each location was determined through an analysis of the underlying fixed asset records in conjunction with the use of industry experience and available market data. Based on the Company’s assessments, for the year ended December 31, 2023, we recorded impairment charges on the Boehlen styrene monomer assets of $0.5 million, which include charges recorded subsequent to March 2020 related to capital expenditures at the facility that we determined to be impaired. The amounts are included within “Impairment and other charges” in the consolidated statements of operations and are all allocated to the Feedstocks segment. Refer to Note 8 for more information.

Through December 31, 2023, we have continued to assess the recoverability of certain assets, and concluded there are no additional significant events or circumstances identified by management that would indicate these assets are not recoverable. However, the current environment is subject to changing market conditions and requires significant management judgment to identify the potential impact to our assessment. If we are not able to achieve certain actions or our future operating results do not meet our expectations, it is possible that impairment charges may need to be recorded on one or more of our operating facilities.

Long-lived assets to be disposed of by sale are classified as held-for-sale and are reported at the lower of carrying amount or fair value less cost to sell, and depreciation is ceased. Long-lived assets to be disposed of in a manner other than by sale are classified as held-and-used until they are disposed. The Company had no assets classified as held-for-sale as of December 31, 2023.

As noted above, our goodwill impairment testing is performed annually as of October 1 at a reporting unit level. We perform more frequent impairment tests when events or changes in circumstances indicate that the fair value of a reporting unit has more likely than not declined below the carrying value.

A goodwill impairment loss generally would be recognized when the carrying amount of the reporting unit’s net assets exceeds the estimated fair value of the reporting unit. When supportable, the Company employs the qualitative assessment of goodwill impairment prescribed by Accounting Standards Codification 350. Otherwise, the estimated fair value of a reporting unit is primarily determined using an income approach (under the discounted cash flow method). Key assumptions and estimates used in the goodwill impairment testing include projections of revenues and EBITDA, the estimated weighted average cost of capital (“WACC”), and a projected long-term growth rate, all of which are based on data available at the time of the testing. The WACC is calculated incorporating weighted average returns on debt and equity from similar market participants, and therefore, changes in the market, which are beyond the control of the Company, may have an impact on future calculations of estimated fair value.

As a result of the goodwill impairment testing performed in the fourth quarter of 2022, the PMMA business and Aristech Surfaces carrying value of their net assets exceeded fair value, resulting in an impairment. All other reporting units had fair values that exceeded the carrying value of their net assets, indicating that no impairment of goodwill is warranted. These reporting units, which are included in the Engineered Materials operating segment, were acquired in 2021 as described in Note 4 in the consolidated financial statements. The impairment charges were attributed to the continuation of the challenging macroeconomic environment experienced in 2022, including significantly lower demand for building & construction and wellness applications, which led to lower operating results including slower growth projections, and a prolonged drop in market capitalization, as well as an increase in the WACC. The Company reduced the carrying value of the PMMA business and Aristech Surfaces reporting units through the recognition of a $226.6 million and $70.5 million non-cash goodwill impairment loss, respectively. These losses are recorded within “Impairment and other charges” on the consolidated statement of operations and are allocated to the Engineered Materials segment.

As of January 1, 2023, the Company realigned the Engineered Materials segment reporting structure. The PMMA business and Aristech Surfaces reporting units were combined with the Legacy Engineered Materials reporting unit to

57

Table of Contents

form the Engineered Materials reporting unit. Impairment assessments on each reporting unit were performed immediately before and after the change in organizational structure where it was concluded there was no goodwill impairment.

During the second quarter 2023, the Company determined that a triggering event had occurred for the Engineered Materials reporting unit indicating it was more likely than not that the fair value of this goodwill was less than the associated carrying value. This determination resulted from the persistence of the challenging operating conditions, customer destocking and underlying demand weakness that contributed to a revised outlook reflecting a further reduction in near-term forecasted operating results, growth projections, as well as an additional decrease in market capitalization. Therefore, the Company performed a goodwill impairment assessment as of June 1, 2023 and recorded a goodwill impairment charge of $349.0 million, reflected within “Impairment and other charges” on the consolidated statement of operations. The Company did not identify any impairment indicators in any of the other reporting units for the year ended December 31, 2023.

As of December 31, 2023, the remaining $63.8 million in total goodwill is allocated to the reportable segments as follows: $44.0 million to Plastics Solutions, $15.4 million to Latex Binders, and $4.4 million to Polystyrene, with no amounts allocated to the Engineered Materials, Feedstocks or Americas Styrenics segments.

Factors which could result in future impairment charges, among others, include changes in worldwide economic conditions, changes in technology, changes in competitive conditions and customer preferences, and fluctuations in foreign currency exchange rates. These factors are discussed in Item 7A—Quantitative and Qualitative Disclosures about MarketRisk and Item 1A— Risk Factors included in this Annual Report.

Income Taxes

We account for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences of temporary differences between the carrying amounts and tax bases of assets and liabilities using enacted rates. The effect of a change in tax rates on deferred taxes is recognized in income in the period that includes the enactment date.

Deferred taxes are provided on the outside basis differences and unremitted earnings of subsidiaries outside of Ireland. All undistributed earnings of foreign subsidiaries and affiliates are expected to be repatriated as of December 31, 2023. Based on the evaluation of available evidence, both positive and negative, we recognize future tax benefits, such as net operating loss carryforwards and tax credit carryforwards, to the extent that realizing these benefits is considered to be more likely than not.

As of December 31, 2023, we had net deferred tax assets of $0.8 million, after valuation allowances of $278.3 million. In evaluating the ability to realize the deferred tax assets, we rely on, in order of increasing subjectivity, taxable income in prior carryback years, the future reversals of existing taxable temporary differences, tax planning strategies and forecasted taxable income using historical and projected future operating results.

For the year ended December 31, 2023, management assessed whether there were any changes in facts and circumstances that would result in any changes to the valuation allowance conclusions reached in the prior years. Management believes there is enough negative evidence to determine that it is no longer more likely than not that the net deferred tax assets will be realized in the Company’s Switzerland subsidiary as of December 31, 2023. Among this evidence is the cumulative loss, magnitude of business losses in 2022 and 2023, current adverse economic conditions, restructuring initiatives and higher financial costs. These negative factors combined with no other tax planning strategies identified that could allow the Company to utilize its deferred tax asset, resulted in management’s decision to establish a full valuation allowance against the net deferred tax asset position in December 2023. Management also believes there is enough negative evidence to determine it is no longer more likely than not that the net deferred tax assets in the Company’s US subsidiaries will be realized as of December 31, 2023. Among this evidence is the losses incurred in recent years, projected cumulative loss into 2024, adverse economic conditions, and higher financial costs. These negative factors combined with no other tax planning identified that could allow the Company to utilize its deferred tax asset, resulted in Management’s decision to establish a full valuation allowance against the net deferred tax asset position in December 2023.

As of December 31, 2023, we had deferred tax assets for tax loss carryforward of approximately $146.6 million, $8.9 million of which is subject to expiration in the years between 2024 and 2028. We continue to evaluate our historical

58

Table of Contents

and projected operating results for several legal entities for which we maintain valuation allowances on net deferred tax assets.

We are subject to income taxes in Ireland, the United States and numerous foreign jurisdictions, and are subject to audit within these jurisdictions. Therefore, in the ordinary course of business there is inherent uncertainty in quantifying our income tax positions. The tax provision includes amounts considered sufficient to pay assessments that may result from examinations of prior year tax returns; however, the amount ultimately paid upon resolution of issues raised may differ from the amounts accrued. Since significant judgment is required to assess the future tax consequences of events that have been recognized in our financial statements or tax returns, the ultimate resolution of these events could result in adjustments to our financial statements and such adjustments could be material. Therefore, we consider such estimates to be critical in preparation of our financial statements.

The financial statement effect of an uncertain income tax position is recognized when it is more likely than not, based on the technical merits, that the position will be sustained upon examination. Accruals are recorded for other tax contingencies when it is probable that a liability to a taxing authority has been incurred and the amount of the contingency can be reasonably estimated. Uncertain income tax positions have been recorded in “Other noncurrent obligations” in the consolidated balance sheets for the periods presented.

Management judgment is required in determining our provision for income taxes, our deferred tax assets and liabilities, and any valuation allowance recorded against our deferred tax assets. The valuation allowance is based on our estimates of future taxable income and the period over which we expect the deferred tax assets to be recovered. Our estimate of future taxable income is based on management’s judgment and assumptions about various factors including historical experience and results, cyclicality of the business, and future industry and macroeconomic conditions and trends. Changes in these assumptions in future periods may require we adjust our valuation allowance, which could materially impact our financial position and results of operations.

Pension Plans and Postretirement Benefits

We have various company-sponsored retirement plans covering substantially all employees. We also provide certain health care and life insurance benefits to retired employees in the United States. The U.S.-based plans provide health care benefits, including hospital, physicians’ services, drug and major medical expense coverage, and life insurance benefits. We recognize the underfunded or overfunded status of a defined benefit pension or postretirement plan as an asset or liability in our consolidated balance sheets and recognize changes in the funded status in the year in which the changes occur through AOCI, which is a component of shareholders’ equity.

A settlement is a transaction that is an irrevocable action that relieves the employer (or the plan) of primary responsibility for a pension or postretirement benefit obligation, and that eliminates significant risks related to the obligation and the assets used to effect the settlement. The Company does not record settlement gains or losses during interim periods when the cost of all settlements in a year is less than or equal to the sum of the service cost and interest cost components of net periodic benefit cost for the plan in that year.

Pension benefits associated with these plans are generally based on each participant’s years of service, compensation, and age at retirement or termination. The discount rate is an important element of expense and liability measurement. We evaluate our assumptions at least once each year, or as facts and circumstances dictate, and make changes as conditions warrant.

We determine the discount rate used to measure plan liabilities as of the December 31 measurement date for the pension and postretirement benefit plans. The discount rate reflects the current rate at which the associated liabilities could be effectively settled at the end of the year. We set our discount rates to reflect the yield of a portfolio of high quality, fixed-income debt instruments that would produce cash flows sufficient in timing and amount to settle projected future benefits.

We use a full yield curve approach in the estimation of the future service and interest cost components of net periodic benefit cost for our defined benefit pension and other postretirement benefit plans by applying the specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. Service cost related to our defined benefit pension plans and other postretirement plans is included within “Cost of sales” and “Selling, general and administrative expenses,” whereas all other components of net periodic benefit cost are included within “Other expense (income), net” in the consolidated statements of operations.

59

Table of Contents

We determine the expected long-term rate of return on assets by performing an analysis of historical and expected returns based on the underlying assets, which generally are insurance contracts. We also consider our historical experience with the pension fund asset performance. The expected return of each asset class is derived from a forecasted future return confirmed by current and historical experience. Future actual net periodic benefit cost will depend on the performance of the underlying assets and changes in future discount rates, among other factors.

The weighted average assumptions used to determine pension plan obligations and net periodic benefit costs are provided below:

​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

​ ​ Non-U.S. Defined ​ U.S. Defined Benefit ​ Other Postretirement ​

​ ​ Benefit Pension Plans ​ Pension Plans ​ Benefit Plans ​

​ ​ December 31, ​ December 31, ​ December 31, ​

Pension and other postretirement plan obligations: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Net periodic benefit costs: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Holding all other factors constant, a 0.25% increase (decrease) in the discount rate used to determine net periodic benefit cost would decrease (increase) 2024 pension expense for our non-U.S. plans by approximately $1.0 million and $(1.1) million, respectively. Holding all other factors constant, a 0.25% increase (decrease) in the long-term rate of return on assets used to determine net periodic benefit cost for our non-U.S. plans would decrease (increase) 2024 pension expense by approximately $0.1 million and $(0.1) million, respectively. Holding all other factors constant, a 0.25% increase or decrease in the discount rate, or the long-term rate of return on assets, used to determine net periodic benefit cost for our U.S. plans would change our 2024 pension expense by less than $0.1 million.

Plan assets totaled $106.5 million and $99.5 million as of December 31, 2023 and 2022. As noted above, plan assets are invested primarily in insurance contracts that provide for guaranteed returns. Investments in the pension plan insurance contracts are valued utilizing unobservable inputs, which are contractually determined based on returns, fees, and the present value of the future cash flows, or cash surrender values, of the contracts, and are classified as Level 3 investments. The Company presents certain pension plan assets valued at net asset value per share as a practical expedient outside of the fair value hierarchy.

Recent Accounting Pronouncements

We describe the impact of recent accounting pronouncements in Note 2 of the consolidated financial statements, included elsewhere within this Annual Report.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

We are exposed to changes in interest rates and foreign currency exchange rates because we finance certain operations through fixed and variable rate debt instruments and denominate our transactions in a variety of foreign currencies. We are also exposed to changes in the prices of certain commodities that we use in production. Changes in these rates and commodity prices may have an impact on future cash flows and earnings. We manage these risks through normal operating and financing activities and, when deemed appropriate, through the use of derivative financial instruments. We do not enter into financial instruments for trading or speculative purposes.

By using derivative instruments, we are subject to credit and market risk. The fair market value of the derivative instruments is determined by using valuation models whose inputs are derived using market observable inputs, including interest rate yield curves, as well as foreign exchange and commodity spot and forward rates, and reflects the asset or liability position as of the end of each reporting period. When the fair value of a derivative contract is positive, the counterparty owes us, thus creating a receivable risk for us. We are exposed to counterparty credit risk in the event of

60

Table of Contents

non-performance by counterparties to our derivative agreements. We minimize counterparty credit (or repayment) risk by entering into transactions with various major financial institutions of investment grade credit rating.

Our exposure to market risk is not hedged in a manner that completely eliminates the effects of changing market conditions on earnings or cash flows.

Interest Rate Risk

Given the Company’s debt structure, we have certain exposure to changes in interest rates. Refer to Note 17 in the consolidated financial statements for further information regarding the Company’s debt facilities.

The Company’s 2028 Refinance Term Loans bear interest at a rate per annum equal to Term SOFR (as defined in the 2028 Refinance Credit Agreement) plus 8.50%, subject to a 3.00% SOFR floor. The Company’s 2028 Term Loan B bears an interest rate of SOFR plus 2.50% (subject to a 0.00% SOFR floor) and is not party to an interest rate swap agreement. The Company’s 2024 Term Loan B bore an interest rate of LIBOR plus 2.00% (subject to a 0.00% LIBOR floor) as of December 31, 2022. Based on weighted average outstanding borrowings under the 2028 Term Loan B and 2028 Refinance Term Loans for the year ended December 31, 2023, an increase in 100 basis points in SOFR would have resulted in approximately $23.8 million of additional interest expense for the period.

Loans under the 2026 Revolving Facility, at the Borrowers’ option, may be maintained as (a) SOFR loans, which bear interest at a rate per annum equal to SOFR plus the applicable margin (as defined in the Credit Agreement), if applicable, or (b) base rate loans which shall bear interest at a rate per annum equal to the base rate plus the applicable margin (as defined in the Credit Agreement). As of December 31, 2023, the Borrowers are required to pay a quarterly commitment fee in respect of any unused commitments under the 2026 Revolving Facility equal to 0.375% per annum. As of and for the year ended December 31, 2023, we had no variable rate debt issued under our 2026 Revolving Facility.

Our Accounts Receivable Securitization Facility is subject to interest charges on both the amount of outstanding borrowings as well as the amount of available, but undrawn commitments under the facility. As of December 31, 2023, the Accounts Receivable Securitization Facility incurs fixed interest charges of 1.65% on outstanding borrowings plus variable commercial paper rates which vary by month and by currency, as outstanding balances can be denominated in euros and U.S. dollars, as well as fixed charges of 0.80% on available, but undrawn commitments. As of and throughout the year ended December 31, 2023, we had no variable debt issued under our Accounts Receivable Securitization Facility, and as such, we incurred no variable rate interest related to this facility during the period.

Foreign Currency Exchange Rate Risks

The Company’s ongoing business operations expose us to foreign currency risks, including fluctuating foreign exchange rates. Our primary foreign currency exposure is the euro-to-U.S. dollar exchange rate, noting that approximately 53% of our net sales were generated in Europe for the year ended December 31, 2023. To a lesser degree, we are also exposed to the exchange rates between the U.S. dollar and other currencies, including, among others, the Chinese yuan, South Korean won, Swiss franc, and New Taiwan dollar. To manage these risks, the Company periodically enters into derivative financial instruments such as foreign exchange forward contracts.

Certain subsidiaries have monetary assets and liabilities denominated in currencies other than their respective functional currencies, which creates foreign exchange risk. Our principal strategy in managing exposure to changes in foreign currency exchange rates is to naturally hedge the foreign currency-denominated liabilities on our consolidated balance sheets against corresponding assets of the same currency such that any changes in liabilities due to fluctuations in exchange rates are offset by changes in their corresponding foreign currency assets. In order to further reduce our exposure, we use foreign exchange forward contracts to economically hedge the impact of the variability in exchange rates on our monetary assets and liabilities denominated in certain foreign currencies. These derivative contracts are not designated for hedge accounting treatment.

The Company also enters into forward contracts with the objective of managing the currency risk associated with forecasted U.S. dollar-denominated raw materials purchases by one of our subsidiaries whose functional currency is the euro. By entering into these forward contracts, which are designated as cash flow hedges, the Company buys a designated amount of U.S. dollars and sells euros at the prevailing market rate to mitigate the risk associated with the fluctuations in the euro-to-U.S. dollar foreign currency exchange rate. The qualifying hedge contracts are marked-to-market at each reporting date and any unrealized gains or losses are included in AOCI to the extent effective, and

61

Table of Contents

reclassified to cost of sales in the period during which the transaction affects earnings or it becomes probable that the forecasted transaction will not occur. As of December 31, 2023, the Company does not have any outstanding forward contracts for the purposes of hedging its exposure to the euro. The Company continues to monitor prevailing rate forecasts and its euro-denominated exposure to determine when to enter into these forward contracts. A 1% change in the euro will impact our annual profitability by approximately $1.5 million on a pre-tax basis.

We have legal entities consolidated in our financial statements that have functional currencies other than the U.S. dollar, our reporting currency. As a result of currencies fluctuating against the U.S. dollar, currency translation gains and losses are recorded in other comprehensive income, primarily as a result of the remeasurement of our euro functional legal entities as of December 31, 2023 and 2022.

Raw Material Price Risk

We purchase certain raw materials such as benzene, ethylene, butadiene, BPA, styrene, MMA, and acetone primarily under short- and long-term supply contracts. The pricing terms for these raw material purchases are generally determined based on commodity indices and prevailing market conditions within the relevant geography. The selling prices of our products are generally based, in part, on the current or forecasted costs of our key raw materials, but are often subject to a predetermined lag period for the pass through of these costs. As such, during periods of significant raw material price volatility, the Company may experience material volatility in earnings and cash flows due to the lag in passing through raw material costs, primarily for benzene, ethylene, butadiene, styrene, MMA, and acetone. Assuming no changes in sales price, volume or mix, a hypothetical 10% change in the market price of our raw materials would have impacted cost of sales by approximately $243.3 million for the year ended December 31, 2023.

We mitigate the risk of volatility in raw material prices where possible by passing changes in raw material costs through to our customers by adjusting our prices or including provisions in our contracts that allow us to adjust prices in such a circumstance or by including pricing formulas which utilize commodity indices. Nevertheless, we may be subject to the timing differences described above for the pass through of these costs. In addition, even when raw material costs may be passed on to our customers, during periods of high raw material price volatility, customers without minimum purchase requirements with us may choose to delay purchases of our materials or, in some cases, substitute purchases of our materials with less costly products. We do not currently enter into derivative financial instruments to manage our price risk relating to our raw material contracts.

Commodity Price Risk

We purchase certain commodities, primarily natural gas, to operate facilities and generate heat and steam for various manufacturing processes, which purchases are subject to price volatility, generally based on commodity indices and prevailing market conditions within the relevant geography. In certain instances, the selling prices of our products are based, in part, on the current or forecasted costs of our key commodities, but are subject to a predetermined lag period for the pass through of these costs. As such, during periods of significant commodity price volatility, the Company may experience material volatility in earnings and cash flows due to the lag in or inability to pass through these commodity costs. Such a period arose in 2023, where the challenging operating conditions, including the ongoing war in Ukraine and the corresponding sanctions and other measures being imposed by various governments impacted global markets, particularly in Europe, lead to high volatility and increased prices for natural gas and other energy supplies.

We mitigate the risk of price fluctuations associated with these commodity purchases where possible by passing changes in commodity costs through to our customers by adjusting our prices or including provisions in our contracts that allow us to adjust prices in such a circumstance or by including pricing formulas which utilize commodity indices. Additionally, as deemed appropriate, we may enter into derivative financial instruments such as commodity swaps, which effectively converts a portion of our natural gas costs into a fixed rate obligation. Certain of these commodity swap agreements are designated as cash flow hedges, and as such, the contracts are marked-to-market at each reporting date and any unrealized gains or losses are included in AOCI to the extent effective, and reclassified to cost of sales in the period during which the transaction affects earnings or it becomes probable that the forecasted transaction will not occur. We may also enter into commodity swap agreements to economically hedge the impact of these price fluctuations, which are not designated for hedge accounting treatment. Inclusive of these hedges, a hypothetical 10% increase in natural gas prices will impact cost of sales by approximately $1.6 million.

62

Table of Contents

Item 8. Financial Statements and Supplementary Data

The financial statements and supplementary data required by Regulation S-X are included in Item 15- Exhibits, Financial Statements Schedules contained in Part IV of this Annual Report.

Item 9. Changes in and Disagreements with Accountants on Accounting and Financial Disclosure

None.

Item 9A. Controls and Procedures

Evaluation of Disclosure Controls and Procedures

Our management is responsible for establishing and maintaining disclosure controls and procedures designed to provide reasonable assurance that information required to be disclosed by us in our reports that we file or submit under the Exchange Act (as defined in Rules 13a-15e and 15d-15(e) of the Securities Exchange Act of 1934, as amended) is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms, and that such information is accumulated and communicated to our management, including our Chief Executive Officer and Chief Financial Officer, as appropriate, to allow timely decisions regarding required disclosures. Our management, with the participation of our Chief Executive Officer and Chief Financial Officer, evaluated the effectiveness of the Company’s disclosure controls and procedures as of December 31, 2023. Based on that evaluation, the Chief Executive Officer and Chief Financial Officer concluded that our disclosure controls and procedures as of the end of the period covered by this Annual Report were effective to provide the reasonable level of assurance described above.

Management’s Annual Report on Internal Control over Financial Reporting

Management is responsible for establishing and maintaining adequate internal control over financial reporting, as defined in Rules 13a-15(f) and 15d-15(f) under the Exchange Act. Internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of the Company’s financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with policies and procedures may deteriorate.

Management conducted an assessment of the Company’s internal control over financial reporting as of December 31, 2023 based on the framework in Internal Control—Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission. Based on the assessment, management concluded that, as of December 31, 2023, the Company’s internal control over financial reporting is effective.

The effectiveness of the Company’s internal control over financial reporting as of December 31, 2023 has been audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm, as stated in their report which appears herein.

Changes in Internal Control over Financial Reporting

In 2021, the Company began a multi-year project to upgrade our legacy ERP environment to an updated version of SAP through a phased implementation approach. Through the fourth quarter of 2023, we have completed the migration of the PMMA business operations, with implementation in the remaining business operations expected to occur in phases over the next several years. In connection with this implementation, we have updated the processes that constitute our internal control over financial reporting, as necessary, to accommodate related changes to our business processes.

The Company believes we have maintained appropriate internal controls during our initial phased implementation period and will continue to evaluate, test and monitor our internal controls over financial reporting for effectiveness as processes and procedures in each of these impacted areas evolve.

63

Table of Contents

Item 9B. Other Information

Trading Arrangements

None of the Company’s directors or officers adopted, modified, or terminated a Rule 10b5-1 trading arrangement or a non-Rule 10b5-1 trading arrangement during the Company’s fiscal quarter ended December 31, 2023.

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

Not applicable.

​

Part III

Item 10. Directors, Executive Officers and Corporate Governance

Except as set forth below, the information required by this Item 10 is incorporated herein by reference from the sections captioned “Election of Directors,” “Corporate Governance,” “Board Structure and Committee Composition,” “Our Company’s Executive Officers,” and “Delinquent Section 16(a) Reports” of the Company’s definitive proxy statement for the 2024 annual general meeting of shareholders to be filed with the SEC pursuant to Regulation 14A under the Securities Exchange Act of 1934 (the “2024 Proxy Statement”).

Code of Ethics

The Company has adopted a Code of Business Conduct applicable to all of our directors, officers and employees, and a Code of Ethics for Senior Financial Employees applicable to our principal executive, financial and accounting officers, and all persons performing similar functions. A copy of each of those Codes is available on the Company’s corporate website at www.trinseo.com under Investor Relations—Corporate Governance—Ethics and Compliance. If we make any substantive amendments to these Codes, or grant any waivers, including any implicit waivers from the provisions of these Codes, we will make a disclosure on our website or in a report on Form 8-K. Our Code of Business of Conduct is supported by a number of support policies which are specifically referenced in the Code, and most of which are also available on our corporate website. Our website and the information contained on that site, or accessible through that site, are not a part of, and are not incorporated by reference into, this Annual Report.

Insider Trading Policy

The Company has adopted an insider trading policy that governs the purchase, sale and/or other dispositions of our securities by our directors, officers and employees, as well as their immediate family members and others who may have access to material nonpublic information concerning the Company, and that is designed to promote compliance with insider trading laws, rules and regulations. The policy prohibits the unauthorized disclosure of any nonpublic information acquired in the workplace, the misuse of material nonpublic information in securities trading. All persons subject to the policy are prohibited from the purchase or sale of our securities except in designated trading windows or pursuant to preapproved 10b5-1 trading plans. Certain persons, including our executive officers and directors, must obtain preclearance prior to any trading in our securities. The policy also prohibits short sales, transactions in publicly traded options such as puts, calls or other derivatives, hedging transactions and other inherently speculative transactions. A copy of our Insider Trading Policy is filed as Exhibit 19.1 to this Annual Report on Form 10-K.

Item 11. Executive Compensation

The information required by this Item 11 will be contained in our 2024 Proxy Statement and is incorporated by reference herein.

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Shareholder Matters

The information required by this Item 12 will be contained in our 2024 Proxy Statement and is incorporated by reference herein.

64

Table of Contents

Item 13. Certain Relationships and Related Transactions, and Director Independence

The information required by this Item 13 will be contained in our 2024 Proxy Statement and is incorporated by reference herein.

Item 14. Principal Accounting Fees and Services

The information required by this Item 14 will be contained in our 2024 Proxy Statement and is incorporated by reference herein.

65

Table of Contents

Part IV

Item 15. Exhibits, Financial Statement Schedules

(a) The following documents are filed as part of this report:

1. Financial statements:

​

Reports of Independent Registered Public Accounting Firms F-2

Consolidated Balance Sheets as of December 31, 2023 and 2022 F-6

​ ​

​

​

2. Exhibits: The exhibits to this report are listed in the exhibit index below.

​

66

Table of Contents

EXHIBIT INDEX

​

​

Exhibit No. ​ Description

​ ​ ​

​ ​ ​

​ ​ ​

4.3 † ​ Description of Securities

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

67

Table of Contents

​

Exhibit No. ​ Description

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

68

Table of Contents

​

Exhibit No. ​ Description

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

69

Table of Contents

​

Exhibit No. ​ Description

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

19.1 † ​ Trinseo PLC Insider Trading Policy

​ ​ ​

21.1 † ​ Subsidiaries of Trinseo PLC

​ ​ ​

​ ​ ​

70

Table of Contents

​

Exhibit No. ​ Description

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

​ ​ ​

97.1 † ​ Trinseo PLC Policy for Recoupment of Incentive Compensation

​ ​ ​

101.INS † ​ iXBRL Instance Document

​ ​ ​

101.SCH † ​ iXBRL Taxonomy Extension Schema Document

​ ​ ​

101.CAL † ​ iXBRL Taxonomy Extension Calculation Linkbase Document

​ ​ ​

101.DEF † ​ iXBRL Taxonomy Extension Definition Linkbase Document

​ ​ ​

101.LAB † ​ iXBRL Extension Label Linkbase Document

​ ​ ​

101.PRE † ​ iXBRL Taxonomy Extension Presentation Linkbase Document

​ ​ ​

​

* Compensatory plan or arrangement.

§§ Certain portions of this exhibit were redacted pursuant to Item 601(b)(10)(iv) of Regulation S-K. The omitted information is (i) not material and (ii) would likely cause us competitive harm if publicly disclosed. We agree to furnish supplementally an unredacted copy of the exhibit to the Securities and Exchange Commission on its request; provided, however that the Company may request confidential treatment of this exhibit pursuant to Rule 24b-2 of the Securities Exchange Act of 1934, as amended.

† Filed herewith.

​

​

Item 16. Form 10-K Summary

None.

71

Table of Contents

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: February 23, 2024

TRINSEO PLC

​ ​ ​

​ By: /s/ Frank Bozich

​ Name: Frank Bozich

​ Title: President and Chief Executive Officer(Principal Executive Officer)

​

72

Table of Contents

Pursuant to the requirements of the Securities Act of 1934, this report has been signed by the following persons in the capacities and on the dates indicated.

Signature Title Date

​ ​

Frank Bozich ​ (Principal Executive Officer) ​

​ ​ ​ ​ ​

David Stasse ​ (Principal Financial Officer) ​

​ ​ ​ ​ ​

Roger E. Greene ​ (Principal Accounting Officer) ​

​ ​

/s/ Joseph Alvarado ​ Director ​ February 23, 2024

Joseph Alvarado ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ Victoria Brifo ​ Director ​ February 23, 2024

Victoria Brifo ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ Jeffrey J. Cote ​ Director ​ February 23, 2024

Jeffrey J. Cote ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ Pierre-Marie De Leener ​ Director ​ February 23, 2024

Pierre-Marie De Leener ​ ​

​ ​

/s/ Jeanmarie Desmond ​ Director ​ February 23, 2024

Jeanmarie Desmond ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ Matthew T. Farrell ​ Director ​ February 23, 2024

Matthew T. Farrell ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ K’Lynne Johnson ​ Chair and Director ​ February 23, 2024

K’Lynne Johnson ​ ​

​ ​

/s/ Sandra Beach Lin ​ Director ​ February 23, 2024

Sandra Beach Lin ​ ​

​ ​ ​ ​ ​

/s/ Henri Steinmetz ​ Director ​ February 23, 2024

Henri Steinmetz ​ ​ ​ ​

​ ​ ​ ​ ​

/s/ Mark Tomkins ​ Director ​ February 23, 2024

Mark Tomkins ​ ​

​

​

73

Table of Contents

INDEX TO CONSOLIDATED FINANCIAL STATEMENTS

​

Audited Consolidated Financial Statements

Report of Independent Registered Public Accounting Firm (PCAOB ID 238) F-2

Report of Independent Registered Public Accounting Firm (PCAOB ID 34) F-5

Consolidated Balance Sheets as of December 31, 2023 and 2022 F-6

​

​

​

F-1

Table of Contents

Report of Independent Registered Public Accounting Firm

​

To theBoard of Directors and Shareholders of Trinseo PLC

​

Opinions on the Financial Statements and Internal Control over Financial Reporting

​

We have audited the accompanying consolidated balance sheets of Trinseo PLC and its subsidiaries (the “Company”) as of December 31, 2023 and 2022, and the related consolidated statements of operations, of comprehensive income (loss), of shareholders' equity and of cash flows for each of the three years in the period ended December 31, 2023, including the related notes and financial statement schedule listed in the accompanying index (collectively referred to as the “consolidated financial statements”). We also have audited the Company’s internal control over financial reporting as of December 31, 2023, based on criteria established in Internal Control – Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission (COSO).

​

In our opinion, based on our audits and the report of other auditors, the consolidated financial statements referred to above present fairly, in all material respects, the financial position of the Company as of December 31, 2023 and 2022, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2023 in conformity with accounting principles generally accepted in the United States of America. Also in our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of December 31, 2023, based on criteria established in Internal Control - Integrated Framework (2013) issued by the COSO.

​

We did not audit the financial statements of Americas Styrenics LLC, a 50% equity investment of Trinseo PLC, which is reflected in the consolidated financial statements of Trinseo PLC as an equity method investment of $252.2 million and $255.1 million as of December 31, 2023 and 2022, respectively, and equity in earnings of unconsolidated affiliates of $62.1, $102.2 and $92.7 for each of the three years in the period ended December 31, 2023, respectively. Those statements were audited by other auditors whose report thereon has been furnished to us, and our opinion expressed herein, insofar as it relates to the amounts included for Americas Styrenics LLC, is based solely on the report of the other auditors.

​

Basis for Opinions

​

The Company's management is responsible for these consolidated financial statements, for maintaining effective internal control over financial reporting, and for its assessment of the effectiveness of internal control over financial reporting, included in Management’s Annual Report on Internal Control over Financial Reporting appearing under Item 9A. Our responsibility is to express opinions on the Company’s consolidated financial statements and on the Company's internal control over financial reporting based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

​

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audits to obtain reasonable assurance about whether the consolidated financial statements are free of material misstatement, whether due to error or fraud, and whether effective internal control over financial reporting was maintained in all material respects.

​

Our audits of the consolidated financial statements included performing procedures to assess the risks of material misstatement of the consolidated financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the consolidated financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the consolidated financial statements. Our audit of internal control over financial reporting included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, and testing and evaluating the design and operating effectiveness of internal control based on the assessed risk. Our audits also included performing

F-2

Table of Contents

such other procedures as we considered necessary in the circumstances. We believe that our audits and the report of other auditors provide a reasonable basis for our opinions.

​

Definition and Limitations of Internal Control over Financial Reporting

​

A company’s internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company’s internal control over financial reporting includes those policies and procedures that (i) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (ii) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (iii) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use, or disposition of the company’s assets that could have a material effect on the financial statements.

​

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

​

Critical Audit Matters

​

The critical audit matter communicated below is a matter arising from the current period audit of the consolidated financial statements that was communicated or required to be communicated to the audit committee and that (i) relates to accounts or disclosures that are material to the consolidated financial statements and (ii) involved our especially challenging, subjective, or complex judgments. The communication of critical audit matters does not alter in any way our opinion on the consolidated financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

​

Interim Goodwill Impairment Assessment – Engineered Materials Reporting Unit

​

As described in Notes 2 and 15 to the consolidated financial statements, goodwill is tested for impairment at the reporting unit level annually, as of October 1, or more frequently when events or changes in circumstances indicate that the fair value of a reporting unit has more likely than not declined below the carrying value. In the second quarter of 2023, management determined that a triggering event for the Engineered Materials reporting unit had occurred indicating it was more likely than not that the fair value of this goodwill was less than the associated carrying value. Management primarily utilizes an income approach (under the discounted cash flow method) to calculate the fair value of its reporting units. As a result of the interim impairment assessment performed, the Company recognized a non-cash goodwill impairment loss of $349.0 million during the three months ended June 30, 2023, which was equal to the full carrying value of the Engineered Materials reporting unit's associated goodwill. As of December 31, 2023, the remaining consolidated goodwill balance was $63.8 million. Key assumptions and estimates used by management in the goodwill impairment testing include projections of revenues and EBITDA, the estimated weighted average cost of capital (“WACC”), and a projected long-term growth rate.

​

The principal considerations for our determination that performing procedures relating to the interim goodwill impairment assessment of the Engineered Materials reporting unit as a critical audit matter are (i) the significant judgment by management when developing the fair value estimate of the Engineered Materials reporting unit; (ii) a high degree of auditor judgment, subjectivity, and effort in performing procedures and evaluating management’s significant assumptions related to projections of revenues and EBITDA, and the WACC; and (iii) the audit effort involved the use of professionals with specialized skill and knowledge.

​

Addressing the matter involved performing procedures and evaluating audit evidence in connection with forming our overall opinion on the consolidated financial statements. These procedures included testing the effectiveness of controls

F-3

Table of Contents

relating to management’s interim goodwill impairment assessment, including controls over the valuation of the Engineered Materials reporting unit. These procedures also included, among others, (i) testing management’s process for developing the fair value estimate of the reporting unit; (ii) evaluating the appropriateness of the discounted cash flow method used by management; (iii) testing the completeness and accuracy of the underlying data used in the discounted cash flow method; and (iv) evaluating the reasonableness of the significant assumptions used by management related to projections of revenues and EBITDA, and the WACC. Evaluating management’s significant assumptions related to projections of revenues and EBITDA involved evaluating whether the assumptions used by management were reasonable considering (i) the current and past performance of the reporting unit; (ii) consistency with external market and industry data; and (iii) whether these assumptions were consistent with evidence obtained in other areas of the audit. Professionals with specialized skill and knowledge were used to assist in evaluating (i) the appropriateness of the discounted cash flow method and (ii) the reasonableness of the significant assumption related to the WACC..

​

/s/ PricewaterhouseCoopers LLP

Philadelphia, Pennsylvania

February 23, 2024

​

We have served as the Company’s auditor since 2010.

​

F-4

Table of Contents

​

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

​

To the Members and the Board of Directors of