Biodegradable Copolyesters of Poly(hexamethylene terephthalate) Containing Bicyclic 2,4:3,5-Di-O-methylene-d-Glucarate Units

A set of copolyesters (PHTxGluxy) with compositions ranging between 90/10 and 50/50 in addition to the parent homopolyesters poly(hexamethylene terephthalate) (PHT) and PHGlux, are prepared by the melt polycondensation of 1,6‐hexanediol (HD) with mixtures of dimethyl terephthalate (DMT) and dimethyl 2,4:3,5‐di‐O‐methylene‐d‐glucarate (Glux). The copolyesters have M¯w in the 35 000–45 000 g mol−1 range, their microstructure is random, and they start to decompose at a temperature well above 300 °C. Crystallinity of PHT is repressed by copoly­merization so that copolyesters containing more than 20% of sugar‐based units are essentially amorphous. On the contrary, PHTxGluxy displays a Tg that increases monotonically with composition from 16 °C in PHT up to 73 °C in PHGlux. Compared with PHT, the copolyesters show an accentuated susceptibility to hydrolysis and are sensitive to the action of lipases upon incubation under physiological conditions. The degradability of PHTxGluxy increases with the content in Glux units. The partial replacement of the tere­phthalate units (T) by bicyclic acetalized glucarate units (Glux) in poly(hexamethylene terephthalate) (PHT) gives rise to biodegradable copolyesters with enhanced Tg. Compared with other cyclic acetalized aldarate units previously explored, the glucarate unit is the one rendering the largest increase in Tg.