Comparison between physical blending and copolymerization of poly(trimethylene carbonate) and poly(adipic anhydride) with special regard to compatibility, morphology and degradation

Blends from poly(trimethylene carbonate) (PTMC) and poly(adipic anhydride) (PAA) with different compositions and different molecular weights were prepared by a solution blending method. Comparing blends with copolymers generally, the original degradation properties of the used components were changed through physical blending (or filling an oligomer as a plasticizer into a polymer), which represents a more convenient, lower cost and composition-controlled method to combine two components with different degradation properties. DSC results show that the T-g of PTMC and T-m of PAA in the blend are lower than those in the homopolymers and they are functions of the molecular weight for PTMC in the blends. SEM micrographs show that a thick dispersion occurs in the blends. The molecular weight of PTMC in the blend obviously decreases as the degradation in vitro proceeds, for the samples of 40% PTMC, M-n drops 39%, M-W drops 12% and the polydispersity increase 44% within 25 days. GC-MS and DSC measurements imply that the depression in molecular weight of PTMC is attributed to the formation of PTMC oligomers from degradation. The results confirmed that the filling of PAA oligomers, which acted as a fast-degraded plasticizer and resulted in an acidic environment, to PTMC could speed up the degradation of PTMC in phosphate buffer solution. Degradation rate and pH of the degradation media change depending on the composition of the blends.