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 molecular weights and polydispersity indices of these polyesters were determined. The physical properties of these polyesters were investigated by thermogravinietric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA). These polymers are semicrystalline except for PSorA, which is amorphous. With increasing sorbitol or glycerol content in the polyesters, both melting and crystallization temperatures decreased. The melting temperature 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 copolymerization with either sorbitol or glycerol. Furthermore, the crystal phase is that of POA.