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 ( n GA ) with M w values of 46,700-50,600 g mol -1 were synthesized via melt polycondensation, and the effects of altering the n GA 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 n GA were synthesized for comparison. DSC analysis revealed that PGBAT21 ( n GA = 21%) and PGBAT92 were semicrystalline, melting between 102.8 and 163.3 °C, while PGBAT44, PGBAT86-89, PGBT80, and PGBS90 were amorphous, with T g values from -19.0 to 23.7 °C. These high n GA 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 n GA copolymers, annealed PGBS90 ( M w 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.