FORM 3
        	UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES
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                      	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	                      	

1. Name and Address of Reporting Person *

Thomas Stephen F.	2. Date of Event Requiring Statement (MM/DD/YYYY)
6/11/2014 
	3. Issuer Name and Ticker or Trading Symbol

Trinseo S.A. [TSE]	
(Last)        (First)        (Middle)

C/O BAIN CAPITAL INVESTORS, LLC, JOHN HANCOCK TOWER, 200 CLARENDON STREET	4. Relationship of Reporting Person(s) to Issuer (Check all applicable)

__ X __ Director                            ___ X ___ 10% Owner
_____ Officer (give title below)          _____ Other (specify below)	
(Street)

BOSTON, MA 02116       

(City)              (State)              (Zip)	5. If Amendment, Date Original Filed (MM/DD/YYYY)

	6. Individual or Joint/Group Filing (Check Applicable Line)

_ X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person	

Table I - Non-Derivative Securities Beneficially Owned	
1.Title of Security
(Instr. 4)	2. Amount of Securities Beneficially Owned
(Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)	4. Nature of Indirect Beneficial Ownership
(Instr. 5)	
Ordinary Shares  	37269567  	I  	See Footnote   (1) (2)	

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)	
1. Title of Derivate Security
(Instr. 4)	2. Date Exercisable and Expiration Date
(MM/DD/YYYY)	3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)	4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)	6. Nature of Indirect Beneficial Ownership
(Instr. 5)	
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares				

Explanation of Responses:	
(  1) 	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"). 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., which is the general partner of Europe Fund III. By virtue of these relationships, BCI may be deemed to share voting and dispositive power with respect to the shares held by BCEM Holding. In addition to being the general partner of Bain Capital Partners Europe III, L.P., which is the general partner of Europe Fund III, BCI is the general partner of Bain Capital Partners X, L.P.,	
(  2) 	(Continued from footnote 1) which is the general partner of Bain Capital Fund X, L.P. BCI is also the managing general partner of BCIP Associates IV, L.P., BCIP Associates IV-B, L.P., BCIP Trust Associates IV, L.P. and BCIP Trust Associates IV-B, L.P. Mr. Thomas is a Principal of BCI. By virtue of the relationships described in this footnote, Mr. Thomas may be deemed to share voting and dispositive power with respect to the shares of Trinseo S.A. held by BCEM Holding. Mr. Thomas disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.	

Reporting Owners	
Reporting Owner Name / Address	Relationships	
	Director	10% Owner	Officer	Other	
Thomas Stephen F.
C/O BAIN CAPITAL INVESTORS, LLC
JOHN HANCOCK TOWER, 200 CLARENDON STREET
BOSTON, MA 02116	X	X			

Signatures		
/s/: Stephen Thomas		6/11/2014	
** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.	
*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).	
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).	
Note:	File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.	
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