Trinseo shareholders elect all 11 directors, approve say-on-pay and incentive plan amendment

The Company’s shareholders approved, on an advisory basis, the compensation paid to the Company’s named executive officers by the votes set forth in the table below: ​ For Against Abstain Broker Non-Votes 26,802,766 1,310,850 34,997 2,614,559

The Company’s shareholders approved the election of eleven director nominees to serve a term expiring at the end of the 2024 annual general meeting of shareholders by the votes set forth in the table below: ​ ​ ​ ​ ​ Name For Against Abstain Broker Non-Votes K’Lynne Johnson 27,542,299 583,967 22,347 2,614,559 Joseph Alvarado 27,422,118 713,440 13,055 2,614,559 Frank Bozich 27,892,015 216,875 39,723 2,614,559 Victoria Brifo 27,881,430 254,747 12,436 2,614,559 Jeffrey Cote 27,922,531 213,542 12,540 2,614,559 Pierre-Marie De Leener 27,884,431 251,636 12,546 2,614,559 Jeanmarie Desmond 27,910,976 225,189 12,448 2,614,559 Matthew Farrell 27,889,955 246,091 12,567 2,614,559 Sandra Beach Lin 27,638,185 497,878 12,550 2,614,559 Henri Steinmetz 27,911,470 216,675 20,468 2,614,559 Mark Tomkins 27,641,973 494,076 12,564 2,614,559

The Company’s shareholders approved the grant of authority of the Company’s Board of Directors to issue shares, by the votes set forth in the table below: For Against Abstain 30,137,502 612,864 12,806

The Company’s shareholders approved the price range for the Company’s re-issuance of treasury shares, as described in the proxy statement, by the votes set forth in the table below: ​ For Against Abstain 30,577,734 156,343 29,095

The Company’s shareholders approved the authority of the Company’s Board of Directors to opt out of statutory pre-emption rights, with respect to up to 10% of issued share capital, by the votes set forth in the table below: ​ ​ For Against Abstain 30,532,641 201,204 29,327

The Company’s shareholders ratified the audit committee’s appointment of PricewaterhouseCoopers LLP to be the Company’s independent registered public accounting firm for the year ending December 31, 2023, and to authorize, by binding vote, the Audit Committee of the Board to set its auditors’ remuneration by the votes set forth in the table below: ​ For Against Abstain 30,514,060 245,323 3,789

The Company’s shareholders approved the amendment to the Company’s Omnibus Incentive Plan, by the votes set forth in the table below. The amended Omnibus Incentive Plan is attached hereto as Exhibit 10.1 . ​ For Against Abstain Broker Non-Votes 21,308,657 6,809,553 30,403 2,614,559