Enhanced Heat Resistance of PPC-P- co -PLA Block Copolymers by Increasing the Crystallinity of the PLA Phase through Transesterification

The relatively low heat resistance of amorphous CO2-based polyester-polycarbonate (PPC-P) retards its application in disposable packaging materials. Here, a kind of PPC-P-co-PLA block copolymers with enhanced heat resistance and high crystallinity of PLA segment was synthesized by a one pot/two-step synthesis method. First, PPC-P was synthesized via ring-opening copolymerization of propylene oxide, phthalic anhydride, and CO2. Subsequently, PPC-P-co-PLA block copolymers were obtained in one pot by transesterification of PPC-P and polylactide (PLA). When the PLA content ranges from 7 wt % to 21 wt %, the molecular weight of the block copolymers is controlled within the range of 74.7 to 88.8 kg/mol. The block copolymer shows a microphase separation structure, and the PLA phase in PPC-P-co-PLA block copolymers crystallizes via heterogeneous nucleation with crystallinity ranges from 35.7 to 58.4% in the PLA segments and from 9.34 to 14.5% for the whole copolymer. The high crystallinity of the PLA segments substantially enhances the heat resistance of the copolymer, achieving a Vicat softening temperature of 52.5 °C and a melting temperature as high as 170 °C. Additionally, the 5% decomposition temperature is elevated by 18 to 30 °C compared to PPC-P. Collectively, this study provides an effective approach to improving the heat resistance of PPC-P while maintaining its high tensile strength of 40 to 50 MPa. The enhanced heat resistance of PPC-P-co-PLA broadens the application of CO2-based biodegradable PPC-P in disposable packaging materials. The synthesis method provides a practical foundation for the preparation of biodegradable block copolymers with high heat resistance.