Physical characterization of sorbitol or glycerol containing aliphatic copolyesters synthesized by lipase-catalyzed polymerization

Copolymers of octanediol adipate and sorbitol adipate, P(OA-SA), copolymers of octanediol adipate and glycerol adipate, P(OA-GA), poly(octamethylene adipate), POA, and poly(sorbitol adipate), PSorA, were synthesized using immobilized Lipase B from Candida antarctica (Novozyme 435) as catalyst. The mol. wts. and polydispersity indexes of these polyesters were detd. The phys. properties of these polyesters were investigated by thermogravimetric anal. (TGA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and dynamic mech. anal. (DMA). These polymers are semicryst. except for PSorA, which is amorphous. With increasing sorbitol or glycerol content in the polyesters, both melting and crystn. temps. decreased. The melting temp. depression is well described by Baur's equation for random copolymers where the second comonomer is completely excluded from the crystal phase of the crystallizable first monomer. Also, the melting enthalpy decreases, and WAXS measurements confirm that the degree of crystallinity decreases upon copolymn. with either sorbitol or glycerol. Furthermore, the crystal phase is that of POA.