THE MODIFICATION OF LACTIC-ACID BASED POLY(ESTER-URETHANE) BY COPOLYMERIZATION

Copolymers of L-lactic acid (LLA) with DL-mandelic acid (DLMA), 4-hydr oxybenzoic acid, 4-acetoxybenzoic acid, DL-malic acid, or anhydrous ci tric acid were synthesized via direct copolycondensation in the presen ce of 1,4-butanediol, using stannous octoate as catalyst. The effect o f the comonomer and the comonomer ratio on polycondensation and the gl ass transition temperature were investigated. The glass transition tem perature of amorphous poly(L-lactic acid-co-DL-mandelic acid) increase d Linearly from 33 degrees to 56 degrees C as the mandelic acid compos ition was increased from 0 to 45 mol %. For urethane synthesis, prepol ymers of LLA and DLMA were condensation polymerized with compositions of 100/0, 90/10, and 80/20 (mol % in feed). The preparation of poly(es ter-urethane) (PEU) was carried out in a stirred glass reactor, using 1,6-hexamethylene diisocyanate and isophorone diisocyanate in melt. Th e glass transition temperature of poly(L-lactic acid-co-DL-mandelic ac id-urethanes) showed a marked increase with increased mandelic acid co mposition. The molecular weights of these urethanes were lower than fo r PEU based on poly(L-lactic acid). Such a depression in the degree of polymerization is attributed to the steric hindrance of the bulky phe nyl group as a side chain of mandelic acid. (C) 1997 John Wiley & Sons , Inc.