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                                                                   EXHIBIT 10.12


                    MASTER INVENTION DISCLOSURE ASSIGNMENT
                    --------------------------------------

          This Agreement, dated March 31, 2001, between Millipore Corporation, a
     Massachusetts corporation having a place of business at 80 Ashby Road,
     Bedford, Massachusetts 01730 ("Millipore") and Mykrolis Corporation, a
     Delaware corporation, having a place of business at Patriots Park, Bedford,
     Massachusetts 01730 ("Mykrolis").

          WHEREAS, the Board of Directors of Millipore Corporation has
     determined that it is in the best interest of Millipore and its
     stockholders to separate Millipore's existing businesses into two
     independent businesses;

          WHEREAS, as part of the foregoing, Millipore and Mykrolis, have
     entered into a Master Separation and Distribution Agreement (as defined
     below) which provides, among other things, for the separation of certain
     Mykrolis assets and Mykrolis liabilities, the initial public offering of
     Mykrolis stock, the distribution of such stock and the execution and
     delivery of certain other agreements in order to facilitate and provide for
     the foregoing;

          WHEREAS, Millipore is the owner via employment agreements from the
     inventor(s) of the inventions described in Invention Disclosures relating
     to the Mykrolis Business (as defined in the Master Separation and
     Distribution Agreement) ("Disclosures"); and

          WHEREAS, Mykrolis is desirous of acquiring said Disclosures.

          NOW, THEREFORE, for good and valuable consideration, the receipt of
     which is hereby acknowledged, MILLIPORE by these presents does sell, assign
     and transfer unto Mykrolis its successors and assigns the full, exclusive
     and worldwide right to all inventions that may arise from the Disclosures
     including the right to file a patent application in the United States of
     America or in countries foreign to the United States of America, and the
     entire right, title and interest in, to and under any Letters Patent which
     may be granted on said inventions, or any parts thereof, or on any
     continuation, division or reissue thereof in the United States of America,
     in the territorial possessions of the United States of America and in any
     country foreign to the United States of America, the same to be held and
     enjoyed by Mykrolis, its successors and assigns as fully and entirely as
     the same would have been held by MILLIPORE, had this assignment not been
     made.

          And MILLIPORE does hereby agree for itself and for its successors and
     assigns to execute any lawful document and to testify as to any material
     fact or thing which Mykrolis, its successors and assigns may deem necessary
     in order to secure unto itself, its successors and assigns the full right,
     title and interest in and to the full enjoyment of all such inventions or
     any part thereof and any Letters Patent that may arise form the
     Disclosures, the same to be done without any further consideration.


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          IN WITNESS WHEREOF, I set my hand this 31st day of March, 2001.

          /s/ Francis J. Lunger
          --------------------------------
                   (Signature)

          Francis J. Lunger
          --------------------------------
                   (Typed Name)

          Executive Vice President, Millipore Corporation
          -----------------------------------------------


          On this day and year aforesaid, before me personally appeared Francis
 J. Lunger, known to me to be the person described in and the person who
 executed the foregoing instrument of assignment and he/she did acknowledge the
 same to be his/her free act and deed.


                               -----------------------------------

                               /s/ Peter W. Walcott
                               ----------------------------------, Notary Public


                               My Commission expires  8/3/01
                                                    ---------------------------

          IN WITNESS WHEREOF, I set my hand this  31st day of March, 2001.

          Jean-Marc Pandraud
          --------------------------------
                    (Signature)

          Jean-Marc Pandraud
          --------------------------------

          President, Mykrolis Corporation
          --------------------------------



          On this day and year aforesaid, before me personally appeared Jean-
 Marc Pandraud , known to me to be the person described in and the person who
 executed the foregoing instrument of assignment and he/she did acknowledge the
 same to be his/her free act and deed.


                               -----------------------------------

                               /s/ Peter W. Walcott
                               ----------------------------------, Notary Public


                               My Commission expires  8/3/01
                                                    ---------------------------


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