Document:

<PAGE>
                                                                     Exhibit 4.1

                                      SIPEX

NUMBER                                                                    SHARES

                                SIPEX CORPORATION

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

COMMON STOCK                                 SEE REVERSE FOR CERTAIN DEFINITIONS
                                                  CUSIP

THIS CERTIFIES THAT

is the owner of

    FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK, $.01 PAR VALUE, OF

                                SIPEX CORPORATION

transferable only on the books of the Corporation by the holder hereof in person
or by duly authorized attorney upon surrender of this certificate properly
endorsed. This Certificate and the shares represented hereby are issued under
and subject to the laws of the State of Delaware and to the certificate of
incorporation and by-laws of the Corporation, as amended from time to time. This
Certificate is not valid unless countersigned and registered by the Transfer
Agent and Registrar.

      IN WITNESS WHEREOF, the Corporation has caused this Certificate to be
signed by the facsimile signatures of its duly authorized officers and a
facsimile of its corporate seal to be hereunto affixed.

Dated                             Corporate Seal
<PAGE>
                               SIPEX Corporation

      The Corporation has more than one class of stock authorized to be issued.
The Corporation will furnish without charge to each stockholder upon written
request, a copy of the full text of the preferences, voting powers,
qualifications and special and relative rights of the shares of each class of
stock (and any series thereof) authorized to be issued by the Corporation.

      The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in fully
according to applicable laws or regulations:

UNIF GIFT MIN ACT -                         Custodian
                    ________________________         _________________
                           (Cust)                          (Minor)

TEN COM -- as tenants in common

TEN ENT --      as tenants by the entireties
JT TEN  --      as joint tenants with right of
                survivorship and not as tenants
                in common

    Additional abbreviations may also be used though not in the above list.

For value received, _______________ hereby sell, assign and transfer unto
    PLEASE INSERT SOCIAL SECURITY
    OR OTHER IDENTIFYING NUMBER
    OF ASSIGNEE

    ____________________________

________________________________________________________________________________
   (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING ZIP CODE OF ASSIGNEE)

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

__________________________________________________________________ shares of the

capital stock represented by the within Certificate, and do hereby irrevocably
constitute and appoint ___________________________ Attorney to transfer the said
stock on the books of the within named Corporation with full power of
substitution in the premises.

Dated
      ___________________

                              (Signature)
                                         _______________________________________
           NOTICE:                       THE SIGNATURE TO THIS ASSIGNMENT MUST
                                         CORRESPOND WITH THE NAME WRITTEN UPON
                                         THE FACE OF THE CERTIFICATE IN EVERY
                                         PARTICULAR, WITHOUT ALTERATION OR
                                         ENLARGEMENT OR ANY CHANGE WHATEVER.

             Signature Guaranteed:
                                  ______________________________________________
                                  ALL GUARANTEES MUST BE MADE BY A FINANCIAL
                                  INSTITUTION (SUCGH AS A BANK OR BROKER)
                                  WHICH IS A PARTICIPANT IN THE SECURITIES
                                  TRANSFER AGENTS MEDALLION PROGRAM ("STAMP"),
                                  THE STOCK YORK STOCK EXCHANGE INC. MEDALLION
                                  SIGNATURES PROGRAM ("MSP") OR THE STOCK
                                  EXCHANGE'S MEDALLION PROGRAM (SEMP") AND MUST
                                  NOT BE DATED. GUARANTEES BY A NOTARY PUBLIC
                                  ARE NOT ACCEPTABLE.<PAGE>
                                                                   Exhibit 10.15

                               SECOND AMENDMENT TO

    SECOND AMENDED AND RESTATED WAREHOUSE REVOLVING CREDIT FACILITY AGREEMENT

      THIS SECOND AMENDMENT TO THE SECOND AMENDED AND RESTATED WAREHOUSE
REVOLVING CREDIT FACILITY AGREEMENT (this "Amendment") is entered into as of
October 16, 2003 and amends in certain respects the Second Amended and Restated
Warehouse Revolving Credit Facility Agreement dated as of August 31, 2001 (as
amended, the "Credit Agreement"), among MARLIN LEASING CORPORATION (the
"Borrower"), each of the financial institutions that is or pursuant to the terms
thereof may become a party thereto as lender (individually, a "Lender" , and
collectively, the "Lenders") and NATIONAL CITY BANK, as Agent for the Lenders
(the "Agent").

                              W I T N E S S E T H:

      WHEREAS, the Borrower and the Lenders wish to make certain changes to the
Credit Agreement subject to the conditions herein set forth.

      NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Agent, the Borrower and the
Lenders hereby agree as follows:

      SECTION 1. Defined Terms. Capitalized terms used herein and not otherwise
defined herein shall have the respective meanings ascribed to them in the Credit
Agreement.

      SECTION 2. Credit Agreement Amendments.

            (a) The definition of "Majority Lenders" in Section 1.01 of the
      Credit Agreement is hereby amended to delete "55%" and substitute "66%" in
      lieu thereof.

            (b) Section 2.01(f) of the Credit Agreement is hereby amended to
      delete "$30,000,000" and to substitute "$37,500,000" in lieu thereof.

            (c) Section 7.14 of the Credit Agreement is hereby amended and
      restated to read as follows:

                  "Section 7.14. Capital Expenditures. Make or be or become
      obligated to make Capital Expenditures in excess of $1,750,000 in the
      aggregate in any fiscal year without the prior written consent of the
      Agent; provided, however, that such limit shall be $3,000,000 for the
      fiscal year during which the Borrower relocates its principal office from
      124 Gaither Drive, Suite 170, Mount Laurel, NJ.

            (d) Effective upon admission of Harris Trust and Savings Bank as an
      Additional Lender, Schedule 1.01 to the Credit Agreement is hereby amended
      and restated to read in its entirety as Schedule 1.01 annexed to this
      Amendment.

            (e) Schedule 3.19 to the Credit Agreement is hereby deleted in its
      entirety and replaced with schedule 3.19 attached hereto.
<PAGE>
            (f) Except as specifically amended or modified above, all of the
      terms of the Credit Agreement shall remain unchanged and in full force and
      effect.

      SECTION 3. Effectiveness. The amendments and consents set forth in Section
2 of this Amendment shall be conditioned upon (a) receipt by the Agent of
counterparts of this Amendment executed by the Borrower and the Majority Lenders
and (b) the fulfillment to the satisfaction of the Agent of each of the
following conditions:

            (i) The Borrower shall have delivered to the Agent in form and
      substance satisfactory to the Agent a Certificate of the Secretary or
      Assistant Secretary of the Borrower certifying (1) that all corporate
      action by the Borrower necessary to authorize the execution, delivery and
      performance of each of the Amendment Documents (as hereunder defined) to
      which it is a party and the transactions contemplated thereby has been
      taken and that such authorization has not been rescinded, limited or
      modified, (2) the incumbency (with specimen signatures) of the Authorized
      Officers of the Borrower, and (3) that all representations and warranties
      set forth in this Amendment are true and correct at and as of the date of
      the effectiveness of this Amendment.

            (ii) The Agent shall have received such other instruments,
      agreements and documents as it shall reasonably require in connection with
      this Amendment and the matters referred to above.

            (iii) All matters related to the financial condition, assets,
      liabilities and creditworthiness of the Borrower shall be satisfactory to
      the Agent and the Lenders, in their sole discretion.

      SECTION 4. Representations and Warranties. In order to induce the Lenders
to execute this Amendment, the Borrower hereby represents and warrants to the
Agent and Lenders as follows, which representations and warranties shall survive
the execution and delivery of this Amendment and the other Amendment Documents
(hereinafter defined):

      (a) The Borrower is a corporation duly organized, validly existing and in
good standing under the laws of Delaware and has the power to own its assets and
to transact the business in which it is currently engaged and in which it
proposes to be engaged.

      (b) The Borrower is duly qualified to do business as a foreign corporation
and is in good standing in each jurisdiction in which its failure to qualify
could have a Material Adverse Effect.

      (c) The Borrower has the power to execute, deliver and perform this
Amendment, any other agreements or documents being or to be executed and
delivered in connection herewith (collectively the "Amendment Documents"). The
Borrower has taken all necessary action (corporate or otherwise) to authorize
the execution, delivery and performance of the Amendment Documents. No consent
or approval of any Person (including, without limitation, any stockholder of the
Borrower), other than any such consent or approval a copy of which has been
delivered to the Agent in form and substance satisfactory to the Agent, no
filing with, action by, consent or approval of any landlord or mortgagee, no
waiver of any Lien or right of distraint or other similar right and no filing
with, action by, consent, license, approval, authorization or declaration of any
governmental authority, bureau or agency, is or will be required in connection

                                       2
<PAGE>
with the execution, delivery or performance by the Borrower or the validity,
enforcement or priority, of the Amendment Documents.

      (d) The execution, delivery and performance by the Borrower of each of the
Amendment Documents to which it is a party will not (i) violate or conflict with
any provision of law or any rule or regulation, (ii) violate or conflict with
any provision of the Amended Articles or by-laws of the Borrower, (iii) violate
or conflict with or result in a breach of any order, writ, injunction,
ordinance, resolution, decree, or other similar document or instrument of any
court or governmental authority, bureau or agency, domestic or foreign, or
create (with or without the giving of notice or lapse of time, or both) a
default under or breach of any agreement, bond, note or indenture to which the
Borrower is a party, or by which it is bound or any of its properties or assets
are affected, or (iv) result in the imposition of any Lien of any nature
whatsoever upon any of its properties or assets owned by or used in connection
with the business of the Borrower, except for the Liens created and granted
pursuant to the Security Documents.

      (e) This Amendment and each of the other Amendment Documents has been or
will be duly executed and delivered by the Borrower, and when executed and
delivered each will constitute the valid and legally binding obligation of the
Borrower, enforceable against it in accordance with its terms, except as such
enforceability may be limited by applicable bankruptcy, insolvency or similar
laws affecting the enforcement of creditors' rights generally or by the
availability of equitable remedies.

      (f) Neither the Borrower nor any of its Subsidiaries is in default under
any agreement, ordinance, resolution, decree, bond, note, indenture, order or
judgment to which it is a party or by which it is bound, or by which any of the
properties or assets owned by it or used in the conduct of its business is
affected, and the Borrower and its Subsidiaries have complied and are in
compliance with all applicable laws, ordinances and regulations, including,
without limitation, Environmental Laws, in either case which default, or
non-compliance with which laws, could have a Material Adverse Effect on the
Borrower.

      (g) The Indebtedness under the Credit Agreement constitutes Senior
Indebtedness under the ING Purchase Agreement, the Wachovia Purchase Agreement
and the Wachovia II Purchase Agreement.

      (h) The Borrower is in full compliance with the terms and conditions of
the Loan Documents, each of the representations and warranties set forth in the
Credit Agreement and the other Loan Documents are true and correct in all
material respects as if made on and as of the date of effectiveness of this
Amendment, and, as of the date of effectiveness of this Amendment and after
giving effect thereto and to the consummation of the transactions contemplated
hereby, no Default or Event of Default has occurred and is continuing.

      (i) Neither the Financial Statements nor any certificate, opinion, or any
other statement made or furnished in writing to the Agent or the Lenders by or
on behalf of the Borrower in connection with this Amendment or the transactions
contemplated hereby, contains any untrue statement of a material fact, or omits
to state a material fact necessary in order to make the statements contained
therein or herein not misleading.

                                       3
<PAGE>
      (j) Any failure of any of the representations and warranties made by
Borrower in this Amendment to be true and correct in all respects when made
shall constitute an Event of Default under the Credit Agreement.

      SECTION 5. Outstanding Indebtedness. Borrower hereby acknowledges
unconditionally that, as of the close of business on October 9, 2003, the
outstanding principal balance of all Revolving Loans is $2,275,430.64. Borrower
acknowledges and agrees that the foregoing balance of the Revolving Loans,
together with accrued and unpaid interest thereon, is owing to Lender without
claim, counterclaim, recoupment, defense or setoff of any kind.

      SECTION 6. Reference to and Effect on Loan Documents.

      (a) On and after the date hereof, each reference in the Credit Agreement
to "this Agreement", "hereunder", "hereof", "herein" or words of like import,
and each reference in the other Loan Documents to the Credit Agreement, shall
mean and be a reference to the Credit Agreement as amended hereby.

      (b) Except as otherwise expressly set forth herein, the execution,
delivery and effectiveness of this Amendment shall not operate as a waiver of
any right, power or remedy of any Lender, or the Agent under the Credit
Agreement or any of the other Loan Documents, shall not constitute a waiver of
any provision of the Credit Agreement or any of the other Loan Documents, nor
shall it affect or diminish any Lender's or the Agent's rights to hereafter
require strict performance of any provision of the Credit Agreement or any of
the other Loan Documents.

      SECTION 7. Reaffirmation of Security Interest. The Borrower hereby
reaffirms as of the date hereof each and every security interest and lien
granted in favor of the Agent and the Lenders under the Loan Documents, and
agrees and acknowledges that such security interests and liens shall continue
from and after the date hereof and shall remain in full force and effect from
and after the date hereof, in each case after giving effect to the Credit
Agreement as amended by this Amendment, and the obligations secured thereby and
thereunder shall include Borrower's obligations under the Credit Agreement as
amended by this Amendment. Each such reaffirmed security interest and lien
remains and shall continue to remain in full force and effect and is hereby in
all respects ratified and confirmed.

      SECTION 8. Further Assurances. Each of the parties hereto hereby agrees to
do such further acts and things and to execute, deliver and acknowledge such
additional agreements, powers and instruments as any other party hereto may
reasonably require to carry into effect the purposes of this Amendment.

      SECTION 9. Governing Law. THE VALIDITY, INTERPRETATION AND ENFORCEMENT OF
THIS AMENDMENT SHALL BE GOVERNED BY THE LAWS OF THE COMMONWEALTH OF PENNSYLVANIA
WITHOUT GIVING EFFECT TO THE CONFLICT OF LAWS PRINCIPLES THEREOF.

      SECTION 10. Counterparts. This Amendment may be executed in any number of
counterparts and by the different parties hereto in separate counterparts, each
of which when so executed and delivered shall be an original, but all of which
shall together constitute one and the same instrument. Execution and delivery of
this Amendment by facsimile transmission shall

                                       4
<PAGE>
constitute execution and delivery of this Amendment for all purposes, with the
same force and effect as execution and delivery of an originally manually signed
copy hereof.

      SECTION 11. Headings; Binding Effect. The headings of the several sections
of this Amendment are inserted for convenience only and shall not in any way
affect the meaning or construction of any provision of this Amendment. The
provisions of this Amendment shall inure to the benefit of and be binding upon
the parties hereto and their respective permitted successors and assigns.

[BALANCE OF PAGE INTENTIONALLY LEFT BLANK; SIGNATURES TO FOLLOW]

                                       5
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their proper and duly authorized officers as of the
date set forth above.

                                       BORROWER

                                       MARLIN LEASING CORPORATION

                                       By: _____________________________
                                            Name:
                                            Title:

                                       LENDERS:

                                       NATIONAL CITY BANK

                                       By:_____________________________
                                            Name:
                                            Title:

                                       FIRSTRUST SAVINGS BANK

                                       By:_____________________________
                                             Name:
                                             Title:

                                       SOVEREIGN BANK

                                       By:_____________________________
                                             Name:
                                             Title:

                                       HARRIS TRUST AND SAVINGS BANK

                                       By:_____________________________
                                             Name:
                                             Title:

                                       AGENT:

                                       NATIONAL CITY BANK, As Agent

                                       By:_____________________________
                                            Name:
                                            Title:
<PAGE>
                                                                   SCHEDULE 1.01

                   COMMITMENT PERCENTAGES AND LOAN COMMITMENTS

<TABLE>
<CAPTION>
         Lender Name                         Loan Commitment      Commitment Percentage(1)
         -----------                         ---------------      ------------------------
<S>                                          <C>                  <C>
National City Bank                             $15,000,000                     37.50%
Sovereign Bank                                 $10,000,000                     25.00%
Firstrust Savings Bank                         $ 7,500,000                     18.75%
Harris Trust and Savings Bank                  $ 7,500,000                     18.75%
                                               -----------               -----------
                 Total                         $40,000,000                    100.00%
</TABLE>

----------

(1)   Figure represents the actual percentage rounded to the nearest
      one-hundredth of one percent.

                                       7

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