X0306 4 2016-08-12 0 0001519061 Trinseo S.A. TSE 0001040508 BAIN CAPITAL INVESTORS LLC 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001607423 Bain Capital Everest Manager Holding SCA 4 LOU HEMMER, L-1748 GRAND-DUCHY OF LUXEMBOURG N4 LUXEMBOURG 0 0 1 0 0001610192 Bain Capital Everest Manager S.a.r.l. 4 LOU HEMMER, L-1748 GRAND-DUCHY OF LUXEMBOURG N4 LUXEMBOURG 0 0 1 0 0001610293 Bain Capital Europe Fund III, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001610292 Bain Capital Partners Europe III, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001417662 Bain Capital Fund X LP 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001525871 Bain Capital Partners X, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001561353 BCIP Associates IV, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001561352 BCIP Associates IV-B, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001610291 BCIP Trust Associates IV, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 ORDINARY SHARES 2016-08-12 4 S 0 8000000 49.15 D 10669567 I See Footnotes Represents ordinary shares of Trinseo S.A. held by Bain Capital Everest Manager Holding SCA ("BCEM Holding"), whose general partner is Bain Capital Everest Manager S.a r.l. ("BCEM"). On August 12, 2016, BCEM Holding sold 8,000,000 Ordinary Shares. Following such sale, BCEM Holding held 10,669,567 Ordinary Shares. All of the outstanding share capital of BCEM is held by Bain Capital Europe Fund III, L.P. ("Europe Fund III") and, in that capacity, Europe Fund III has the power to appoint the managers of BCEM. Bain Capital Investors, LLC ("BCI") is the general partner of Bain Capital Partners Europe III, L.P. ("Partners Europe III"), which is the general partner of Europe Fund III. BCI is also the general partner of Bain Capital Partners X, L.P. ("Partners X"), which is the general partner of Bain Capital Fund X, L.P. ("Fund X"). Boylston Coinvestors, LLC is the general partner of BCIP Associates IV, L.P. ("BCIP IV"), BCIP Associates IV-B, L.P. ("BCIP IV-B"), BCIP Trust Associates IV, L.P. ("BCIP Trust IV") and BCIP Trust Associates IV-B, L.P. ("BCIP Trust IV-B," and, together with BCEM Holdings, BCEM, Europe Fund III, Partners Europe III, Fund X, Partners X, BCIP IV, BCIP IV-B and BCIP Trust IV, the "Bain Capital Entities"). The governance, investment strategy and decision-making process with respect to the investments held by all of the Bain Capital Entities is directed by BCI's Global Private Equity Board. As a result, BCI may be deemed to share voting and dispositive power with respect to the shares of Trinseo S.A. held by BCEM Holding. BCI disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. 1 of 2 BAIN CAPITAL EVEREST MANAGER HOLDING SCA, By: Bain Capital Everest Manager S.a.r.l., its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Manager 2016-08-16 BAIN CAPITAL EVEREST MANAGER S.a.r.l., By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Manager 2016-08-16 BAIN CAPITAL EUROPE FUND III, L.P., By: Bain Capital Partners Europe III, L.P., its general partner, By: Bain Capital Investors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Managing Director 2016-08-16 BAIN CAPITAL PARTNERS EUROPE III, L.P., By: Bain Capital Investors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Managing Director 2016-08-16 BAIN CAPITAL FUND X, L.P., By: Bain Capital Partners X, L.P., its general partner, By: Bain Capital Investors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Managing Director 2016-08-16 BAIN CAPITAL PARTNERS X, L.P., By: Bain Capital Investors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Managing Director 2016-08-16 BCIP ASSOCIATES IV, L.P., By: Boylston Coinvestors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Authorized Signatory 2016-08-16 BCIP ASSOCIATES IV-B, L.P., By: Boylston Coinvestors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Authorized Signatory 2016-08-16 BCIP TRUST ASSOCIATES IV, L.P., By: Boylston Coinvestors, LLC, its general partner, By: /s/ Stephen Thomas, Name: Stephen Thomas, Title: Authorized Signatory 2016-08-16