Experimental and Theoretical Study on Glycolic Acid Provided Fast Bio/Seawater-Degradable Poly(Butylene Succinate-<i>co</i>-Glycolate)

Abstract

The very slow degradation of biodegradable polymers in the marine environment is due to the lack of dedicated degradation enzymes in open seas. As a result, introducing monomers that have a fast hydrolysis process is required to accelerate seawater degradation. Poly(butylene succinate-co-glycolate) (PBSGA) copolyesters with glycolic acid (GA) units ranging from 5 to 40% were synthesized by our newly developed polymerizing method based on oligo(glycolic acid). The results of 1H-NMR and GPC revealed that short GA segments were evenly distributed between BS segments, obtaining random copolyesters with a weight-average molecular weight over 6.24 * 104 g/mol. The copolymerized GA units hinder its crystallization capability and increase hydrophilicity of the PBSGAs, which still displayed mechanical properties comparable or even better than most biodegradable polymers. Fast degradation in seawater and enzymatic environments (Candida antarctica lipase B enzymes) is proved experimentally. The quick decomposition in seawater was originated from accelerated hydrolysis. For instance, the weight loss of PBSGA40 (compositions of GA units) exceeded 22% after 49 days. Possible degradation mechanisms were proposed based on Fukui function analysis and frontier molecular orbital calculation. Additionally, the energy barrier for hydrolysis was calculated by the density functional theory method, indicating that the hydrolysis of the polymer chain became more and more easy with the increase in GA units. At last, the addition of GA units only had a mild effect on the shelf life of the PBSGAs.