Synthesis of Poly(D-Lactic Acid) Using a 2-Steps Direct Polycondensation Process

A two steps direct polycondensation process of poly(D-lactic acid) (PDLA) synthesis was studied. The melt- polymerization was combined with esterification using p-Toluenesulfonic acid without addition of metal catalyst. The pre-polymer product from the first step was subsequently subjected to solid-state polymerization (SSP) under high temperature and reduced pressure. Prior to the SSP process, the pre-polymer was characterized its thermal property to detect the crystallization temperature (Tc). The pre-polymers were annealed at temperature Tc for 2 h until the crystallization peak disappeared. The SSP of pre-polymers was carried out for 30 h to produce the satisfied thermal property and high molecular weight. The synthesized poly(D-lactic acid) showed melting temperature of 177oC, weight average molecular weight of 33,300 Da, and decomposition temperature of 255oC.