Poly(glycolic acid) materials with melt reaction/processing temperature window and superior performance synthesized via melt polycondensation

Abstract

Poly(glycolic acid) (PGA) is a biodegradable polyester with ultra-high rigidity, strength and gas barrier properties but very poor toughness. Its high melting temperature (Tm) and very poor thermal stability make it lack temperature window (TW) for reaction and processing, and therefore, synthesis and processing of PGA materials, especially via melt copolycondensation, is still a great challenge to date. In this study, glycolic acid (GA) was copolymerized with small amount of ε-caprolactone (CL) via melt polycondensation to synthesize random poly(glycolic acid-co-ε-caprolactone) (PGC) copolymers with greatly reduced Tm to obtain TW, avoiding serious thermal decomposition during melt polycondensation and processing. Through such a synthetic strategy, PGCs with intrinsic viscosity of 0.7–0.9 dL/g, slight color and controlled composition were successfully synthesized and melt-processed. PGC12–15 display poly(L-lactide)-comparable Tm (160–180 °C), rapid crystallization (crystallinity 26–30 %) and greatly improved ductility (elongation at break of 90–220 % vs. 2.1 % of PGA), and superior or comparable modulus, strength and gas barrier properties when compared with typical polymers commonly used for packaging materials and mulch films. It is the first time that PGA material with processing temperature window, high molecular weight and superior performance has been successfully synthesized by melting polycondensation.