Sugar-based aromatic copolyesters: a comparative study regarding isosorbide and diacetalized alditols as sustainable comonomers

Three carbohydrate-based bicyclic diols, 1,4:3,6-dianhydro-D-glucitol (isosorbide, Is), 2,3:4,5-di-O-methylene-galactitol (Galx) and 2,4:3,5-di-O-methylene-D-mannitol (Manx), were made to react in the melt and under the same conditions with dimethyl terephthalate and 1,4-butanediol to produce respectively three series of PB(x)Is(y)T, PB(x)Galx(y)T and PB(x)Manx(y)T random copolyesters. Five different copolymerizations, with molar feed ratios of 1,4-butanediol to sugar-based diols of 90 : 10, 80 : 20, 70 : 30, 60 : 40 and 50 : 50, were carried out for each bicyclic diol in order to make a comparative study on their reactivity and properties of the resulting copolyesters. Molecular weights and compositions data of the copolyesters revealed the greater facility of diacetalized diols to react under these conditions compared to isosorbide. The three bicyclic diols contributed to increase the thermal stability and also the glass-transition temperature of PBT. The replacement of 40% of 1,4-butanediol by sugar-based diols increased the glass transition temperature of PBT from 31 degrees C to similar to 60 degrees C in the case of Galx and up to similar to 90 degrees C regarding Is and Manx. All PB(x)Galx(y)T copolyesters as well as PB(x)Is(y)T and PB(x)Manx(y)T ones with contents of Is and Manx of up to 32% and 41%, respectively, were semicrystalline.