Sec Form 4 Filing - Arroyo Santiago @ MOMENTA PHARMACEUTICALS INC - 2020-02-07

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Arroyo Santiago 2. Issuer Name and Ticker or Trading Symbol MOMENTA PHARMACEUTICALS INC [ MNTA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP, Chief Medical Officer (Last) (First) (Middle) C/O MOMENTA PHARMACEUTICALS, INC., 301 BINNEY STREET 3. Date of Earliest Transaction (MM/DD/YY) 02/07/2020 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Stock Units ( 1 ) 02/07/2020 A 52,500 ( 2 ) ( 3 ) ( 3 ) Common Stock 52,500 $ 0 52,500 D Stock Option (Right to Buy) $ 31.87 02/07/2020 A 105,000 ( 4 ) ( 5 ) 02/07/2030 Common Stock 105,000 $ 0 105,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Arroyo Santiago C/O MOMENTA PHARMACEUTICALS, INC. 301 BINNEY STREET CAMBRIDGE, MA02142 SVP, Chief Medical Officer Signatures /s/ R. Mark Chamberlin as attorney in fact 02/11/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each Restricted Stock Unit represents a contingent right to receive one share of MNTA common stock. ( 2 )Represents restricted stock units granted by the issuer pursuant to the issuer's 2013 Incentive Award Plan, as amended and restated. ( 3 )Subject to the officer's continued service, the restricted stock units will vest with respect to 25% of the shares on the first anniversary of the grant date, and the remainder will vest in equal quarterly installments over the subsequent three years. ( 4 )Represents options granted by the issuer pursuant to the issuer's 2013 Incentive Award Plan, as amended and restated. ( 5 )Subject to certain criteria, the stock option will vest and become exercisable with respect to 25% of the shares on the first anniversary of the grant date, and the remainder will vest in equal quarterly installments over the subsequent three years.

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 4(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).

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