The effect of glass transition temperature on the crystallization of ε-caprolactone-styrene diblock copolymers

Abstract

The morphology and melting behaviour of ε-caprolactone-styrene diblock copolymers (PCL- b-PS) quenched from the melt were investigated by small-angle X-ray scattering and differential scanning calorimetry as a function of glass transition temperature of the PS block, T g, PS . A plasticizer miscible only with the PS block, such as polystyrene oligomer or dioctyl phthalate, was added to PCL- b-PS in order to decrease T g, PS successively (plasticizer-added PCL- b-PS). The crystallizability of the PCL block depended strongly on T g, PS ; the PCL block did not crystallize when T g, PS was higher than the crystallization temperature T c , while it crystallized partially when T g, PS was lower than T c . However, details of the morphology formed (i.e. the long spacing and lamellar thickness) were independent of T g, PS . These results suggest that the mobility of PCL- b-PS influences extremely the crystallizability of the PCL block, but not the resulting morphology. The morphologies formed in the plasticizer-added PCL- b-PS were compared with those of PCL- b-PS cast from toluene or cyclohexane solution, and the characteristics of these morphologies were qualitatively discussed.