Poly(L-lactic acid)-polyethylene glycol-poly(L-lactic acid) triblock copolymer: A novel macromolecular plasticizer to enhance the crystallization of poly(L-lactic acid)

Different from traditional small molecular plasticizers, poly(L-lactic acid) (PLLA)-polyethylene glycol (PEG)-PLLA triblock copolymers were synthesized by ring-opening polymerization of L-lactide on the end hydroxyls of PEG and blended with PLLA, to enhance the crystallization of PLLA. Non-isothermal and isothermal crystallization studies show that the triblock copolymer enhances the crystallization of PLLA due to the nucleation effect from PLLA segments and the plasticization effect from PEG segments, which strongly depends on the structure of copolymers. With shorter PLLA segment and longer PEG segment of the triblock copolymer, the glass transition temperature and cold crystallization temperature of the blends decrease, and the degree of crystallinity and spherulite growth rate increase owing to the higher content of PEG. However, triblock copolymers with relatively longer PLLA segment and shorter PEG segment show unique nucleation effects for PLLA, leading to the elevation of crystallization temperature of PLLA. The results confirm that the crystallization acceleration of PLLA can be ascribed to the nucleation and plasticization effect, and the plasticization effect is more significant. What's more, the introduction of triblock copolymers improves the compatibility and durability due to the good interfacial interaction with PLLA matrix even at a high loading.