Crystallization Process in Binary Blends of Poly(ε-caprolactone)-block-Polybutadiene Copolymers

Abstract

The crystallization process in binary blends of poly(e-caprolactone)-block-polybutadiene (PCL-b-PB) copolymers has been investigated by time-resolved small-angle X-Ray scattering with synchrotron radiation (SR-SAXS), where the crystallization of PCL blocks induces a morphological transition both in neat copolymers but the crystallization rate is extremely different between them. The microdomain structure in the melt and the final morphology after crystallization were also measured by conventional SAXS, and the melting behavior of crystallized samples was observed by differential scanning calorimetry (DSC). The binary blend forms a single microdomain structure in the melt over the whole composition range investigated, and the crystallization proceeds with an intermediate rate between those of the constituent PCL-b-PB copolymers to result in a single lamellar morphology. The time dependence of SR-SAXS curves is qualitatively similar in features to that for the crystallization of pure PCL-b-PB copolymers, suggesting that the crystallization of the blend is substantially controlled by a single crystallization mechanism. The remarkable change in the crystallization rate with composition is ascribed to the difference in the stability of preexisting microdomain structures. The conformation of (longer and shorter) PB blocks in the final lamellar morphology is qualitatively discussed.