An article entitled "Synthesis, thermo-mechanical and rheological properties of biodegradable long chain branched PBST copolyesters" published in Ind Eng Chem Res (2014)
Biodegradable long chain branched (LCB)
poly(butylene succinate-co-butylene
terephthalate) (PBST) copolyesters were prepared via a two-step
direct esterification 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 LCB PBSTs were characterized and the
thermal, mechanical and rheological properties were investigated.
With increasing DGT loading, PBSTs with higher branching
degree, broader molecular weight distribution and lower melt flow index were
synthesized in shorter polycondensation time. Branching
of PBSTs results in slight decrease in crystallizability, melting and Vicat
softening temperatures, but leads to obvious decrease in elongation at break.
On the other hand, the existence of LCB greatly improved the rheological
properties of PBSTs.
PBST with higher branching degree possesses
higher storage and loss modulus, higher zero-shear viscosity, longer relaxation
time, more obvious shear-thinning, and lower loss
angle tangent.
Han plot of the rheological data also indicate
higher
elasticity of LCB PBSTs.