Synthesis and Characterization of Poly(propylene oxide-lactide) Diblock Copolymer

Different molar ratios of poly(propylene oxide-lactide) diblock copolymers were synthesized from low unsaturated poly(propylene oxide) triols and L- or DL-lactide monomers. The structure of the copolymers was determined by means of FTIR, H-1 NMR and GPC, and the thermal behavior was characterized by DSC and TGA. The results turned out that poly(propylene oxide-L-lactide) (POLLA) or poly(propylene oxide-DL-lactide) (PODLA) diblock copolylmers were synthesized by ring-opening polymerization of lactide with poly(propylene oxide) triol. The POLLA diblock copolymers were semi-crystal line copolymers, and the crystallinity was increased with the increase of LLA segments. However, the PODLA diblock copolymers were amorphous ones. The glass transition temperature of the copolymers was influenced by the composition of the copolymers, and the tested T-g was between the values of the two homopolymers. Compared with poly(propylene oxide), the thermal stability of the diblock copolymers was improved. The thermal decomposition temperature of the copolymers was between 235 and 262 degrees C, which was 30-60 degrees C higher than that of poly(propylene oxide). The results also showed that the chemical structures of various diblock copolymers had an effect on the thermal decomposition kinetic of samples. The mechanism of thermal oxidative decomposition of PODLA was observed in a high temperature region.