Synthesis of poly(lactic acid) with two positively charged chain ends

Abstract

Poly(L-lactic acid)s having two positively charged chain ends were synthesized by chemical reaction between telechelic PLLA and glycidyltrimethylammonium chloride (GTMAC). In order to compare the reactivity of hydroxyl and carboxyl end groups toward the reaction with GTMAC, two types of telechelic PLLA chains- one with two hydroxyl (PLLA-diOH) and the other with two carboxyl chain ends- (PLLA-diCOOH) were synthesized and used in the reaction. The results obtained by nuclear magnetic resonance (NMR) spectroscopy analysis, revealed that the dicarboxyl end groups of PLLA provided more percentage of GTMAC substitution (up to 90%) than that of the PLLA with hydroxyl end groups (19%). This was because protonation on the epoxide ring by the carboxyl end group helped increase the degree of GTMAC substitution. Changes of polymer hydrophilicity were assessed by means of air-water contact angle measurement of solvent cast films. The contact angle was reduced up to 20% when the positively charged PLLA was blended with a commercial PLLA in a ratio of 2:3 by weight. After immersion of powdered positively charged polymers in phosphate buffer pH 7.4 at 37 ºC, percentage decrease of Mn (GPC) at the end of the 4th week of the positively charged PLLA derived from PLLA-COOH (PLLA-COOH+) was 18% while that of the positively charged PLLA derived from PLLA-OH (PLLA-OH+) were insignificantly different. Thermal properties of both two types of the positively charged PLLA were similar to PLLA-diCOOH and PLLA-diOH, respectively.