Effects of Copolymer Composition on the Crystallization and Morphology of Poly(ε-caprolactone)-block-Polystyrene

The morphology and melting behavior of poly(ε-caprolactone)-block-polystyrene (PCL-b-PS) copolymers, quenched from the melt or cast from the toluene solution, were investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) as a function of copolymer composition. The glass transition temperature of PS blocks is higher than the melting temperature of PCL blocks, Tm,PCL, in this system, so that the molecular motion is extremely restricted when the PCL block crystallizes in temperatures below Tm,PCL. DSC results showed that the quenched PCL-b-PS did not crystallize at any temperature when PCL vol%, φPCL, was less than 26%, whereas it crystallized partially when φPCL≥34% and the crystallinity increased with increasing φPCL, suggesting that φPCL affects significantly the crystallizability of PCL blocks. However, crystallization was observed for all PCL-b-PS copolymers cast at 20°C, and the crystallinity decreased appreciably with increasing the casting temperature. SAXS results revealed that high crystallinity PCL-b-PS copolymers had an intensity peak arising from the lamellar morphology, an alternating structure consisting of crystalline lamellae and amorphous layers, whereas low crystallinity PCL-b-PS copolymers did not show any SAXS peak, indicating the morphological difference among crystallized PCL-b-PS copolymers. The morphology formed in PCL-b-PS is discussed as a function of φPCL in terms of the lamellar morphology observed for crystalline homopolymers.