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Exhibit 31.3

CERTIFICATION OF CHIEF EXECUTIVE OFFICER

I, Frank Bozich, certify that:

1.

I have reviewed this Amendment No. 1 to the annual report on Form 10-K/A of Trinseo PLC;

2.

Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

Date: April 27, 2026

By:

/s/ Frank Bozich

Name:

Frank Bozich

Title:

Chief Executive Officer