LACTIC-ACID BASED POLY(ESTER-URETHANES) - USE OF HYDROXYL TERMINATED PREPOLYMER IN URETHANE SYNTHESIS

We studied a two step process for lactic acid polymerization: in the f irst step, the lactic acid is condensation polymerized to a low molecu lar weight hydroxyl terminated prepolymer and then the molecular weigh t is raised by joining prepolymer chains together using diisocyanate a s the chain extender. The resulting polymer is a thermoplastic poly(es ter-urethane). The polymer samples were carefully characterized with C -13-NMR, GPC, DSC, and IR. The results indicate that high conversions of lactic acid can be achieved, as well as independent control of the stereostructure, long chain branches, molecular weight average, and mo lecular weight distribution. Lactic acid is converted into a poly(este r-urethane) with a weight average molecular weight as high as 390,000 g/mol and a glass transition temperature of 53.7 degrees C. The analyz ed content of the monomer in the prepolymer is less than 1 mol % and t he lactide content 2.4 mol %, while the final poly(ester-urethane) is essentially monomer and lactide free. The mechanical properties of the poly(ester-urethane) are comparable to those of polylactides. (C) 199 7 John Wiley & Sons, Inc.