Document:

<PAGE>

                                                                    May 21, 2002
Mr. Thomas O. Pyle
One Devonshire Place, Apt #3701
Boston, MA  02109

Dear Tom:

This letter is to confirm that the following options to acquire the Common Stock
of Millipore Corporation granted to you under the Millipore Corporation 1999
Stock Option Plan for Non-Employee Directors (the "99 Option Plan") have been
converted into options to acquire the number of shares of Common Stock, $0.01
par value, of Mykrolis Corporation at the exercise price specified in the table
below. These converted options are subject to the terms of this letter
agreement, of the 99 Option Plan and of the original grant letter with the
exception that Mykrolis Corporation is substituted for Millipore Corporation
and, as specified below, the options cover shares of Mykrolis Corporation.

<TABLE>
<CAPTION>

--------- --------------- --------------- ----------------- ---------------- ----------------
                             Original     Unvested Options  Post Conversion   Post-Conversion
Grant #   Grant Date      Exercise Price     on 2/27/02     Exercise Price   Unvested Options
--------- --------------- --------------- ----------------- ---------------- ----------------
<S>       <C>             <C>             <C>               <C>              <C>
006878    April 16, 1998      $35.625             500           $6.5602            2,715
--------- --------------- --------------- ----------------- ---------------- ----------------
007383    April 22, 1999     $29.9375            1,000          $5.5129            5,431
--------- --------------- --------------- ----------------- ---------------- ----------------
007899    April 27, 2000     $69.9375            1,500         $12.8787            8,146
--------- --------------- --------------- ----------------- ---------------- ----------------
008549    April 25, 2001      $56.30             2,000         $10.3674           10,861
--------- --------------- --------------- ----------------- ---------------- ----------------
</TABLE>

The above conversions have been determined by calculating the relationship (the
"ratio") of the closing price of Millipore common stock on the NYSE on the
spin-off date (February 27, 2002) [$57.02] to the opening price of Mykrolis
common stock on the NYSE on the first trading day after the spin-off (February
28, 2002) [$10.50]. This ratio [5.43047611] was multiplied times the number of
Millipore shares covered by each of your unvested options to yield the number of
Mykrolis shares covered by the post conversion option; the ratio was then
divided into the exercise price of each of your Millipore unvested options to
yield the exercise price of the post conversion option. These calculations were
designed to preserve the "intrinsic value" of your pre-spin Millipore options in
the converted options immediately after the spin. For example, your 1998
unvested option grant had an intrinsic value of $10,697.50 as of the close of
trading on the NYSE on February 27, 2002 [(500 X MIL FMV of $57.02) - (500 X
original exercise price of $35.625) = $10,697.50] and that option had the same
intrinsic value as of the opening of trading on the NYSE on February 28, 2002
[(2,715 X MYK FMV of $10.50) - (2,715 X post conversion exercise price of
$6.5602) = $10,697.50].

<PAGE>
Mr. Thomas O. Pyle
May 21, 2002
Page 2

All of the above converted options will expire on August 9, 2006 in accordance
with and subject to the provisions of the 99 Option Plan. Under the 99 Option
Plan all outstanding stock options normally are cancelled upon the resignation
of a director. There is an exception, however, where the director resigns with
the consent of Millipore Corporation, a special exercise period of up to 5 years
is established. Accordingly, upon your resignation from the Millipore Board of
Directors on August 9, 2001 your unvested Millipore options were held in
suspense until the spin-off date when they were converted into Mykrolis options
as described above.

Your converted options will vest in annual increments on the date of the Annual
Meeting of the Board of Directors of Mykrolis Corporation in accordance with the
following schedule:

<TABLE>
<CAPTION>
--------- --------------- ----------------- ------------------- ------------------- ------------------
                           Vest on Annual    Vest on Annual      Vest on Annual      Vest on Annual
Grant #   Grant Date      Meeting Date 2002 Meeting Date 2003   Meeting Date 2004   Meeting Date 2005
--------- --------------- ----------------- ------------------- ------------------- ------------------
<S>       <C>             <C>               <C>                 <C>                 <C>
006878    April 16, 1998       2,715           Fully Vested        Fully Vested       Fully Vested
--------- --------------- ----------------- ------------------- ------------------- ------------------
007383    April 22, 1999       2,715              2,716            Fully Vested       Fully Vested
--------- --------------- ----------------- ------------------- ------------------- ------------------
007899    April 27, 2000       2,715              2,715               2,716           Fully Vested
--------- --------------- ----------------- ------------------- ------------------- ------------------
008549    April 25, 2001       2,715              2,715               2,715               2,716
--------- --------------- ----------------- ------------------- ------------------- ------------------
</TABLE>

Please acknowledge receipt of this letter by signing and returning the enclosed
copy of this letter to the address below. It is necessary for us to receive this
signed acknowledgement before any of the converted options may be exercised.

                                                Very truly yours,

                                                MYKROLIS CORPORATION

                                                 C. William Zadel

                               Chairman of the Board and Chief Executive Officer

Please return the signed copy of this letter to:

Ms. Gloria Williams
Mykrolis Corporation
129 Concord Road
Billerica, MA 01821

Receipt and acceptance of the foregoing is hereby acknowledged:

---------------------------------------          ---------------------
               Signature                                 Date<PAGE>

                                                                    EXHIBIT 10.9

                      TECHNICAL COMMUNICATIONS CORPORATION

                               FIRST AMENDMENT TO

                    AMENDED AND RESTATED EMPLOYMENT AGREEMENT

                                       OF

                               CARL H. GUILD, JR.

     This Amendment to the Amended and Restated Employment Agreement is entered
into on November 8, 2001 by and between Technical Communications Corporation, a
Massachusetts corporation (the "Company"), with a principal place of business at
100 Domino Drive, Concord, Massachusetts 01742, and Carl H. Guild, Jr., the
Company's Chief Executive Officer.

     The Company and Executive entered into an Amended and Restated Employment
Agreement effective as of November 19, 1998 (the "Employment Agreement"). The
parties to the Employment Agreement have agreed to certain modifications to the
terms and provisions of the Employment Agreement and desire to amend the
Employment Agreement to reflect those modifications.

     NOW, THEREFORE, in consideration of the premises and mutual promises made
herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the undersigned hereby agree as
follows:

1.   Amendment to Employment Agreement. The Employment Agreement is hereby
amended, effective as of the date hereof, by adding Sections 2.6 and 2.7 as
follows:

     "2.6 In the event of a Change in Control (as hereinafter defined) of the
Company where you (i) resign within Twenty four (24) months after such an event,
or (ii) are terminated without Cause by the Company within twenty four (24)
months after such an event, any unvested option shares held by you shall
automatically vest and become immediately exercisable, and you shall be entitled
to receive Severance Pay in an amount, payable in a lump sum within thirty (30)
days after the effective date of such resignation or termination equal to twenty
four (24) months' Base Salary at the then current level (as set forth on Exhibit
A attached hereto), less applicable taxes, other required withholdings, and any
amounts you may owe the Company, plus all accrued but unpaid expenses and
vacation time (the "Change in Control Payment"). In the event that any payment
to be received by you pursuant to this Section 2.6 or the value of any
acceleration right in any Company stock options you may hold in connection with
the Change in Control of the Company would be subject to an excise tax pursuant
to Section 4999 of the Internal Revenue Code of 1986, as amended (the "Code"),
whether in whole or in part as a result of being an "excess parachute payment"
within the meaning of such terms in Section 280G (b) of the Code, the amount
payable under this Section 2.6 shall be increased (grossed up) to cover the
excise tax liability due under the Section 4999 of the Code. Notwithstanding the
preceding sentence, (a) no portion of such Change in Control Payment or any
acceleration right which tax counsel, selected by the Company's independent
auditors and

<PAGE>

acceptable to you, determines not to constitute a "parachute payment" within
meaning of Section 280G(b) (2) of the Code will be taken into account and (b) no
portion of the Change in Control Payment which tax counsel, selected by the
Company's independent auditors and acceptable to you, determined to be
reasonable compensation for services rendered within the meaning of Section
280G9b) (4) of the Code will taken into account.

     2.7 For purposes of Section 2.6 the term "Change in Control" shall mean the
occurrence of any of the following:

          (a) any person or entity, including a "group" as defined in Section
     13(d) of the Securities Exchange Act of 1934, as amended, other than the
     Company, a wholly owned subsidiary of the Company, or any employee benefit
     plan of the Company or its subsidiaries, becomes the beneficial owner of
     the Company's securities having fifty-one percent (51%) or more of the
     combined voting power of the then outstanding securities of the Company
     that may be cast for the election for directors of the Company; or

          (b) as the result of, or in connection with, any cash tender or
     exchange offer, merger or other business combination, sale of assets or
     contested election or any combination of the foregoing transactions, less
     than a majority of the combined voting power of the then outstanding
     securities of the Company or any successor corporation or entity entitled
     to vote generally in the election of directors of the Company or such other
     corporation or entity after such transaction, are held in the aggregate by
     holders of the Company's securities entitled to vote generally in the
     election of directors of the Company immediately prior to such transaction;
     or

          (c) the approval of the stockholders of the Company of a plan of
     liquidation."

2.   Entire Agreement. Except for the provisions added hereby, the remainder of
the terms and provisions of the Employment Agreement shall remain in full force
and effect. The Employment Agreement and this Amendment, together with the
documents referred to therein and herein, constitute the entire agreement
between the parties hereto pertaining to the subject matter thereof and hereof.

3.   Counterparts. This Amendment may be executed in one or more counterparts,
each of which shall be deemed an original but all of which together will
constitute one and the same instrument.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

<PAGE>

     IN WITNESS WHEREOF, this Agreement has been executed as a sealed instrument
by the Company, by its duly authorized representative, and by Carl H. Guild,
Jr., as of the date first above written.

TECHNICAL COMMUNICATIONS CORPORATION

By:  /s/ Robert T. Lessard         May 13, 2002
     ----------------------------------------------------
     Robert T. Lessard, Director, duly authorized

     /s/ Carl H. Guild Jr.         May 13, 2002
     ----------------------------------------------------
     Carl H. Guild, Jr.

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