Synthesis of High Molecular Weight Poly(L-Lactic Acid)s by Direct Polycondensation with Organic Acids as Catalyst

摘要

In this study, high molecular weight (HMW) poly (L-lactic acid)s (PLLAs) were synthesized by direct polycondensation using organic acid catalysts alone in a nitrogen-controlled environment. The melting point and enthalpy of the pre-polymer produced by melt polycondensation increased as molecular weight grew during solid-state polycondensation. It was observed that the nitrogen-controlled external environment had lower molecular weight than air, but the low molecular weight tail was significantly reduced, as indicated by gel permeation chromatography. This is because it inhibited the reverse reaction by preventing the penetration of water inside the reactor. Also, the control of moisture improved the color of PLLA. The amount of organic acid catalyst used was 1 wt%, which was favorable for achieving HMW. Both p-toluenesulfonic acid and 4-ethylbenzenesulfonic acid are examples of organic acids that were able to produce HMW PLLA.