Synthesis of Star-Comb Double Crystalline Diblock Copolymer of Poly(epsilon-caprolactone)-block-poly( L-lactide): Effect of Chain Topology on Crystallization Behavior

摘要

A series of highly branched star-comb poly(epsilon-caprolactone)-block-poly(L-lactide) (scPCL-b-PLLA) are successfully achieved using star-shaped hydroxylated polybutadiene as the macroinitiator by a simple "grafting from" strategy. The ration of each segment can be controlled by the feed ratio of comonomers. These star-comb double crystalline copolymers are well-defined and expected to illustrate the influences of the polymer chain topology by comparing with their counterparts in linear-shaped, star-shaped, and linear-comb shape. The crystallization behaviors of PCL-b-PLLA copolymers with different architectures are investigated systematically by means of wide-angle X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy analysis. It is shown that the comb branched architectures promote the crystallization behavior of each constituent significantly. Both crystallinity and melting temperature greatly raise from linear to comb-shaped copolymers. Compared to linear-comb topology, the star-comb shape presents some steric hindrance of the graft points, which decrease the crystallinity of scPCL-b-PLLA. Effects of copolymer composition and chain topology on the crystallization are studied and discussed.