Synthesis, Characterization and Degradation of Novel Biodegradable Poly(butylene-co-hexamethylene carbonate) Copolycarbonates

A series of high molecular weight poly(butylene-co-hexamethylene carbonate) (PBHC) copolycarbonates were synthesized by copolymerizations of dimethyl carbonate (DMC), 1,4-butanediol (BD) and 1,6-hexanediol (HD) via a two-step melt polycondensation method. Microstructure analysis determined by high-resolution C-13-NMR showed that butylene carbonate (BC) units and hexamethylene carbonate (HC) units of the synthesized copolymers take a random distribution along the polymer chains. Analyses of the formed byproducts indicated that sublimation of oligomer and thermal degradation of polymer happen during the aliphatic polycarbonate polycondensation. The thermal properties and crystalline structure of the copolymers were studied by DSC, TGA and WAXD. WAXD patterns showed that the copolymers with 11 and 91 mol% HC units form poly(butylene carbonate) (PBC) and poly(hexamethylene carbonate) (PHC) crystals, respectively, while the three other copolymers with intermediate HC unit contents are completely amorphous. The results indicated that the BC and HC units are incompatible in each crystal lattice, and that cocrystallization cannot take place. TGA results indicated that the thermal stability of the obtained PBHC random copolymers is higher than that of PBC and increases with increasing the HC unit content. The enzymatic degradation study revealed that the biodegradation rate of the PBHC copolymers mainly depends not only on the degree of crystallinity and melting temperature but also on the type of crystalline structure, while the composition and microstructure dependences of biodegradability are negligible.