Synthesisand Thermomechanical and Rheological Propertiesof Biodegradable Long-Chain Branched Poly(butylene succinate-co-butyleneterephthalate) Copolyesters.

Biodegradable long-chain branched(LCB) poly(butylene succinate-co-butyleneterephthalate) (PBST) copolyesters were prepared via a two-step directesterification and melt polycondensation process, using a small amount(0–2 mol %) of diglycidyl 1,2,3,6-tetrahydrophthalate (DGT)as an in situ branching agent (BA). The chemical structures of LCBPBSTs were characterized and the thermal, mechanical, and rheologicalproperties were investigated. With increasing DGT loading, PBSTs withhigher branching degree, broader molecular weight distribution, andlower melt flow index were synthesized in shorter polycondensationtime. The branching of PBSTs results in a slight decrease in crystallizability,melting, and Vicat softening temperatures, but leads to an obviousdecrease in elongation at break. On the other hand, the existenceof LCB greatly improved the rheological properties of PBSTs. PBSTwith higher branching degree possesses higher storage and loss modulus,higher zero-shear viscosity, longer relaxation time, more obviousshear-thinning, and lower loss angle tangent. The Han plot of therheological data also indicates higher elasticity of LCB PBSTs. [ABSTRACT FROM AUTHOR]