Synthesis and properties of poly(L-lactide)-polyether-poly(L-lactide) triblock copolymers

Abstract

In this study, the influence of the copolymer composition and the soft segment molecular weight on the physical properties of poly(L-lactide)-polyether-poly(L-lactide) triblock copolymer are investigated. The triblock copolymers were synthesized by ring opening polymerization of L-lactide monomer using PTMG as the initiator. Copolymer having 5wt%, 10wt%, 15wt% PTMG (mol.wt.; 2000-6000) were synthesized. The comparison between the measured Mn by $^1H$-NMR and the theoretical Mn considering the yield shows good agreement in all the samples. By the TGA analysis, thermal stability of the copolymer is evaluated. To determine the other thermal properties, DSC measurements have been carried out to see the structural effect on $T_c$, $T_m$ and the degree of crystallinity. Enhancement of tensile strength and impact strength of compression molded copolymers was observed. To evaluate the effect of the soft segment domain size in the copolymer on mechanical properties, morphology of the copolymer before and after annealing was investigated by AFM. The effect of catalyst concentration and temperature on thermal degradation during synthesis and processing was observed by isothermal TGA. The PLLA-polyether-PLLA triblock copolymer with low catalyst concentration was prepared by injection molding to enhance the thermal stability during the synthesis and processing. The improvement of tensile strength and elongation at break of the copolymer was observed. The impact strength of the block copolymer was also enhanced when compared to neat PLLA.