Synthesis and Characterization of High Glycolic Acid Content Poly(glycolic acid-co-butylene adipate-co-butylene terephthalate) and Poly(glycolic acid-co-butylene succinate) Copolymers with Improved Elasticity

Poly(glycolic acid) (PGA) is a biodegradable polymer with high gas barrier properties, mechanical strength, and heat deflection temperature. However, PGA's brittleness severely limits its application in packaging, creating a need to develop PGA-based copolymers with improved elasticity that maintain its barrier properties and hydrolytic degradability. In this work, a series of PGBAT (poly(glycolic acid-co-butylene) adipate-co-butylene terephthalate) copolymers containing 21-92% glycolic acid (nGA) with Mw values of 46,700-50,600 g mol-1 were synthesized via melt polycondensation, and the effects of altering the nGA on PGBAT's thermomechanical properties and hydrolysis rate were investigated. Poly(glycolic acid-co-butylene succinate) (PGBS) and poly(glycolic acid-co-butylene terephthalate) (PGBT) copolymers with high nGA were synthesized for comparison. DSC analysis revealed that PGBAT21 (nGA = 21%) and PGBAT92 were semicrystalline, melting between 102.8 and 163.3 °C, while PGBAT44, PGBAT86-89, PGBT80, and PGBS90 were amorphous, with Tg values from -19.0 to 23.7 °C. These high nGA copolymers showed similar rates of hydrolysis to PGA, whereas those containing <50% GA showed almost no mass loss over the testing period. Their mechanical properties were highly dependent upon their crystallinity and improved significantly after annealing. Of the high nGA copolymers, annealed PGBS90 (Mw 97,000 g mol-1) possessed excellent mechanical properties with a modulus of 588 MPa, tensile strength of 30.0 MPa, and elongation at break of 171%, a significant improvement on PGA's elongation at break of 3%. This work demonstrates the potential of enhancing PGA's flexibility by introducing minor amounts of low-cost diols and diacids into its synthesis.