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                                                                     EXHIBIT 4.4

                         [DONLAR CORPORATION LETTERHEAD]



February 25, 2002


CONFIDENTIAL

Dr. Robert Gale Martin
c/o Carolina Eye Associates
2170 Midland Road
South Pines, NC 28387

Dear Dr. Martin:

         Currently, you own convertible debt of Donlar Corporation ("Donlar") in
the face amounts and conversion rates listed on Exhibit A, attached hereto (the
"Convertible Notes"), and non-convertible debt of Donlar in the amount listed on
Exhibit B, attached hereto (the "Non-Convertible Note"). This letter agreement
(this "Letter Agreement") sets forth the certain understandings between Dr.
Robert Gale Martin, an individual ("Martin"), and Donlar, an Illinois
corporation, regarding a Bridge Facility to be provided to Donlar and its
subsidiary, Donlar Biosyntrex Corporation, a Nevada corporation ("Biosyntrex")
(Donlar and Biosyntrex are referred to collectively in this Letter Agreement as
the "Company") by Tennessee Farmers Insurance Company or one of its affiliates
("Tennessee Farmers").

         Specifically, this Letter Agreement sets forth the terms upon which
Martin shall (i) surrender all of the Convertible Notes and the Non-Convertible
Note for shares of convertible preferred stock of Donlar; (ii) relinquish the
right to receive any royalty payments from Donlar for shares of common preferred
stock; (iii) surrender for cancellation any warrants Martin holds to purchase
shares of common stock of Donlar for a new warrant to purchase shares of common
stock; and (iv) vote all of Martin's common shares of Donlar in favor of a
merger between Donlar and Biosyntrex.

         Accordingly, Martin and Donlar hereby agree as follows:

         1.       Pursuant to terms and conditions of the Summary of the Terms
                  and Conditions for Proposed Bridge Financing (the "Term
                  Sheet"), attached hereto as Exhibit C, Martin shall:

                  a)   Surrender for cancellation the Convertible Notes and
                       Non-Convertible Note to Donlar in exchange for shares of
                       convertible preferred stock of the Company




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                      in the face amount of $9 million, convertible into
                      approximately 13,235,294 shares of common stock of the
                      Company;

                  b)   Relinquish all rights to receive any royalty payments
                       from Company in exchange for 5,000,000 shares of common
                       stock of the Company;

                  c)   Surrender for cancellation any warrants Martin holds to
                       purchase shares of stock of Donlar, in exchange for a
                       warrant to purchase 3,000,000 shares of common stock of
                       the Company;

                  d)   Execute a subordination agreement acceptable to the
                       lenders under the Bridge Facility, as described in
                       Section III.N.7 of the Term Sheet; and

                  e)   Extend maximum cooperation to the Company and Tennessee
                       Farmers in achieving all of the foregoing in the shortest
                       time possible (in recognition that Martin shall benefit
                       both directly and in directly from the Bridge Facility
                       provided by Tennessee Farmers to the Company).

         2.       Upon the event of a merger between Donlar and Biosyntrex,
                  Martin agrees to vote all of his shares of voting stock of the
                  Company held by him in favor of such merger.

         3.       You acknowledge that Tennessee Farmers is an express third
                  party beneficiary of this letter agreement and shall have all
                  of the claims, rights, powers and remedies of such a third
                  party beneficiary to the maximum extent permitted under
                  applicable law.

         If the foregoing is in accordance with your understanding of our
agreement, please sign where indicated below and deliver a copy of this Letter
Agreement as provided for herein, whereupon this Letter Agreement shall
represent a binding agreement between us and shall be governed by the internal
laws of the State of Illinois.


                                                     Very truly yours,

                                                     DONLAR CORPORATION


                                                     By:
                                                        ------------------------
                                                        Name: Larry Koskan
                                                        Title: President and CEO