A Mild Method to Prepare High Molecular Weight Poly(butylene furandicarboxylate-co-glycolate) Copolyesters: Effect of Glycolate Content on Thermal, Mechanical, Barrier Properties and Biodegradability

The melt polycondensation of glycolic acid based copolymers with high molecular weight remains as a big challenge. In this work, poly(butylene furandicarboxylate-co-glycolate) (PBFGA) and poly(butylene furandicarboxylate)-b-poly(glycolic acid) (PBF-b-GA) copolyesters were synthesized via melt oligomer polycondensation and melt bulk transesterification, respectively. Herein, melt oligomer polycondensation is a better method with mild preparation condition and products with higher molecular weight (Mw). The analysis of GPC demonstrated that PBFGAs possessed Mw up to 8.95×104 g/mol. The PBFGAs also possessed excellent thermal stability (>320 °C), which endowed the copolymers with wider processing window than thermolabile PGA. DSC analyses displayed that PBFGA40-PBFGA10 were semi-crystalline materials that melted between 84.5 and 156 °C, while the PBFGA50-60 were amorphous. Tensile tests indicated high elastic modulus of 524-1262 MPa, tensile strength of 16-44 MPa and good elongation at break over 220% of PBFGAs, exceeding most biodegradable packaging materials. The increase of GA units slightly impacted the barrier properties, with reduced CO2 (53×) and O2 (15×) permeability coefficients than commercial PBAT films, and also better than PET. The hydrolysis of glycolate was restrained by steric hindrance of furan rings, while in enzymatic degradation PBFGAs displayed obvious weight loss with GA units > 20 mol%. With superior thermal, tensile, barrier and degradable properties, PBFGAs have the potential to serve as promising and innovative bio-based polymers for eco-friendly and sustainable plastic packaging.