Thermal behavior and spherulitic superstructures of SBC triblock copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(epsilon-caprolactone) (C) block

The dynamic crystallization and the melting behavior of polystyrene-block-poly(epsilon-caprolactone) (PS-b-PCL, short notation SC), polybutadiene-block-poly(epsilon-caprolactone) (PB-b-PCL, BC) and polystyrene-block-polybutadiene-block-poly(epsilon-caprolactone) (PS-b-PB-b-PCL, SEC) have been studied using differential scanning calorimetry. The copolymers with high molecular weight exhibit microphase separation into microphases consisting of polystyrene, polybutadiene and poly(epsilon-caprolactone) and partial crystallization of the corresponding PCL block. The crystallization occurs at temperatures below the PS glass transition. Depending on the block copolymer composition, Crystallization takes place through a combination of heterogeneous and homogeneous nucleation. Isothermal crystallization was studied in order to determine the equilibrium melting point, T-m(0), of the PCL block, which depends on the weight ratio W-PB:W-PCL The crystallization kinetics was analyzed in terms of Avrami equation. A general decrease in the overall crystallization rate in the block copolymers relative to the equivalent PCL homopolymer was found. Additionally, the growth rate of the spherulites was followed using polarized optical microscopy. Depending on the composition and flexibility of the block connected to PCL, some copolymers showed ring-banded spherulites.