Carbohydrate-based copolyesters made from bicyclic acetalized galactaric acid

Abstract

Mixtures of the dimethyl esters of adipic acid and 2,3:4,5-di-O-methylene-galactaric acid (Galx) were made to react in the melt with either 1,6-hexanediol or 1,12-dodecanediol to produce linear polycyclic copolyesters with aldarate unit contents varying from 10 up to 90 mole %. The copolyesters had weight–average molecular weights in the ∼35,000–45,000 g mol−1 range and a random microstructure, and were thermally stable up to nearly 300 °C. They displayed Tg in the -50 to -7 °C range with values largely increasing with the content in galactarate units. All the copolyesters were semicrystalline with Tm between 20 and 90 °C but only those made from 1,12-dodecanediol were able to crystallize from the melt at a crystallization rate that decreased as the contents in the two comonomers approached each other. Copolyesters containing minor amounts of galactarate units adopted the crystal structure characteristic of aliphatic polyesters but a new crystal polymorph was formed when the cyclic sugar units became the majority. Stress–strain parameters were sensitively affected by composition of the copolyesters with the mechanical behavior changing from flexible/ductile to stiff/brittle with the replacement of adipate units by the galactarate units.