Bio-based PBT copolyesters derived from D-glucose: influence of composition on properties

Two series of bio-based PBT copolyesters were obtained by polycondensation in the melt of 2,4: 3,5-di-Omethylene-D-glucitol (Glux-diol) or dimethyl 2,4: 3,5-di-O-methylene-D-glucarate (Glux-diester) with 1,4-butanediol and dimethyl terephthalate. The glucose-based bicyclic compounds used as comonomers were synthesized from commercially available 1,5-D-gluconolactone. The prepared PBT copolyesters had weight-average molecular weights in the 30 000-50 000 range; they had a random microstructure, and they were stable above 300 degrees C. The copolyesters containing less than 30% of sugar-based units were semicrystalline and were found to adopt the triclinic structure of PBT. These copolyesters with low contents in Glux were able to crystallize from the melt but at lower rates than PBT. The T-g value of PBT steadily increased with the incorporation of Glux units in the polyester chain with an increasing ratio of similar to 1.7 degrees C or similar to 1 degrees C per % Glux point, depending on which unit, the diol or the diacid, was replaced. The copolyesters hydrolyzed at higher rates than PBT, and those containing glucarate units displayed an appreciable susceptibility towards biodegradation.