A journey across the solid state polymerization to assess the role of critical factors influencing the molecular weight of polylactic acid

Abstract

Solid state polymerization (SSP) offers an effective route for synthesizing green polymers with variable molecular weights depending on polymerization condition. In this work, critical factors governing the molecular weight of polylactic acid (PLA) in the course of SSP are manipulated systematically and their contributions to the efficiency of SSP process are discussed. The initial molecular weight of the prepolymer formed, the degree of crystallinity of prepolymer, and the SSP time are changed and analyzed for their effects through different analyses including differential scanning calorimetry, gel permeation chromatography, and Fourier‐transform infrared spectroscopy techniques. It was observed that PLA having highest molecular weight would be the result of formation of a prepolymer having low‐molecular weight, as detected by the analysis of functional group concentration. For the optimized sample, the rate of mass loss in SSP was 12,263 g/mol.day and a crystallinity drop over the hydrolysis process was 3.14 per day. The crystallinity of prepolymers was optimized at ca. 26% in regard with the PLA showing the highest molecular weight. J. VINYL ADDIT. TECHNOL., 25:165–171, 2019. © 2018 Society of Plastics Engineers