POLYMERIZATION OF AQUEOUS LACTIC-ACID TO PREPARE HIGH-MOLECULAR-WEIGHT POLY(LACTIC ACID) BY CHAIN-EXTENDING WITH HEXAMETHYLENE DIISOCYANATE

In order to synthesize the high molecular weight poly(lactic acid) [PL A], Hexamethylene diisocyanate [HDI] was used as a chain extender conn ecting the terminal group of polymers. Poly(lactic acid) of high molec ular weight, 76000 (M(w)) and 33000 (M(n)), was obtained by using anti mony trioxide catalyst after chain-extending with HDI. Without chain-e xtending, the molecular weight of PLA was about 7000 (M(n)). T-m in th e 2nd-scan DSC thermogram was not found when PLA was chain-extended wi th HDI. In order to check the degree of crystallization of polymers, a nnealing of these polymers was carried out at 120 degrees C. Peaks of XRD (X-Ray Diffraction) were sharpened as the duration of annealing wa s lengthened. The analysis of polymers reacted with HDI by H-1-NMR sho wed the broad peaks at 1.32 and 3.14 ppm assigned to HDI units. The mo lecular weight of polymers increased with the increase in the mole rat io of -NCO/-OH.