Synthesis and characterization of triblock copolymer PLA-b-PBT-b-PLA and its effect on the crystallization of PLA

A series of poly(L-lactide)-b-poly(butylene terephthalate)- b-poly(L-lactide) (PLA-b-PBT-b-PLA) triblock copolymers were synthesized via ring-opening polymerization of L-lactide with hydroxyl-functionalized poly(butylene terephthalate) (HOPBT) as macroinitiator and stanneous 2-ethylhexanoate (Sn(Oct)2) as the catalyst in 1,1,2,2-tetrachloroethane (TCE). The conversion of L-lactide was high and the PLA block in the copolymers showed high optical purity. Chemical structure and physical properties of the triblock copolymers were studied using NMR, GPC, DSC, and WAXD. The block structure of the copolymers was confirmed using NMR, and each block formed the same crystal type as the respective homopolymer, i.e., PLA or PBT as revealed by DSC and WAXD. The copolymer, even at a very low content (5 wt%), showed an unexpected favoring effect on the crystallization of PLA, which made it a potential polymeric nucleating agent for PLA.