Renewable Sugar-Based Diols with Different Rigid Structure: Comparable Investigation on Improving Poly(butylene succinate) Performance

In order to improve the mechanical and oxygen barrier properties of poly(butylene succinate) (PBS), two series of sugar-containing PBS copolyesters with different molecular stiffness were synthesized and comparatively investigated, in which a cyclic alditol, isosorbide (Is) or 2,3-O-isopropylidene-L-threitol (ITh) was, respectively, used as a comonomer. Both cyclic alditols were easily available from biomass feedstock, such that Is is a bicyclic compound derived from D-glucose, and ITh is a monocyclic acetalized compound coming from naturally occurring L-tartaric acid. All these copolyesters containing up to 30 mol % of sugar-based units had satisfactory number-average molecular weights in the 16 000-83 000 g mol(-1) range, and presented a random microstructure together with excellent thermal stability. The sugar-containing copolyesters were all semicrystalline and still possessed the monoclinic crystal structure of PBS. The incorporation of either Is or ITh units with rigid cyclic structure into PBS chain decreased the crystallinity and crystallization rate of PBS, while it enhanced its glass transition temperature. In addition, the partial replacement of 1,4-butanediol by sugar-based units endowed PBS with steadily enhanced hydrophilicity. Depending on the type and content of sugar units, the copolyesters show different oxygen barriers and mechanical properties. It was found that copolyester with bicyclic Is sugar units exhibited a better oxygen barrier and mechanical property than that with monocyclic ITh units.