Degradation and physical properties of aliphatic copolyesters derived from mixed diols

Abstract

The effects of molecular structure and composition of poly(butylene succinate) (4-4 polyester derived from succinic acid and 1,4-butane diol) rich random copolyesters on the physical properties and hydrolytic degradation were investigated. Three series of copolyesters, poly(butylene succinate-co-ethylene succinate), poly(butylene succinate-co-propylene succinate), and poly(butylene succinate-co-butyne succinate) were synthesized using ethylene glycol (EG), propylene glycol (PG), and cis-2-butene-1,4-diol (BeD) as a comonomer, respectively up to 40 mol% of diols in the feeds in combination with 1,4-butane diol (BD) and succinic acid (SA). The copolymers were characterized for composition, inherent viscosity, molecular weight, density, thermal properties, and mechanical strength. The melting temperature of copolymers decreased almost linearly at the rate of 1.2-1.6K mol%-1 of ethylene succinate and propylene succinate in the test range. Remarkable improvements in ultimate strain were attained through the copolymerization using EG or PG as a comonomer. It was found that the hydrolytic degradation behaviors of copolyesters conducted in pH 12 alkali solution were greatly affected by the chemical structure and composition of copolymers. The degradation rate of poly(butylene succinate-co-ethylene succinate) consistently increased with the content of ethylene succinate, whereas poly(butylene succinate-co-butyne succinate) showed an adverse effect. The copolymers comprising propylene succinates showed a composition dependancy on the hydrolytic susceptibility ascribable to the conflicting effects between steric hinderance due to methyl substituents and reduced crystallinity.