Biodegradable aromatic copolyesters made from bicyclic acetalized galactaric acid

Abstract

Random poly(hexamethylene terephthalate-co-galactarate) s and poly(dodecamethylene terephthalate-co-galactarate) s copolyesters covering the whole range of compositions were obtained with weight-average molecular weights of 30,000–50,000 g mol 1 by melt polycondensation. They were thermally stable above 300 C, and displayed Tg in the þ20 to 20 C range with values steadily decreasing with the content in galactarate units. All the copolyesters were semicrystalline with Tm between 50 and 150 C and those made from dodecanediol were able to crystallize from the melt at a crystallization rate depending on composition. Copolyesters containing up to 50% of galactaric units retained the crystal structure of their respective polyterephthalate homopolyesters, whereas they adopted the structure of the respective polygalactarates when the content in Galx units reached 70%. Stress-strain essays revealed decay in the mechanical parameters as the aromatic units were replaced by Galx. Incubation in aqueous buffer revealed that hydrolysis of the polyesters were largely enhanced by copolymerization and evidenced the capacity of the Galx unit for making aromatic polyesters susceptible to biodegradation. A detailed NMR analysis complemented by SEM observations indicated that hydrolysis took place by preferred splitting of galactarate ester bonds with releasing of alkanediol and Galx-diacid.