Temperature Dependence of Crystallization Behavior in a Phase-Separated Blend of Poly(ε-caprolactone) Homopolymer and Poly(ε-caprolactone)-block-Polybutadiene Copolymer

The crystallization behavior in a macroscopically phase-separated blend consisting of poly(ε-caprolactone) homopolymer (PCL) and PCL-block-polybutadiene copolymer (PCL-b-PB) is investigated both by synchrotron small-angle X-ray scattering (SR-SAXS) and polarized optical microscope (POM) as a function of crystallization temperature Tc. The characteristic size of the phase-separated structure ξ existing in this blend before crystallization can arbitrarily be controlled by changing the phase separation time. When the blend with ξ=2.5 μm is quenched into various Tc, two scattering peaks are observed in the SR-SAXS curve during crystallization, which arise from the crystallized PCL and PCL-b-PB regions. The growth rates of these scattering peaks are identical at lower Tc (≤35 °C), while they deviate gradually with increasing Tc. Only one type of spherulites is observed for the blend with ξ=10 μm crystallized at Tc=35 °C to give a single growth rate, while two different types of spherulites appear at higher Tc (≥40 °C) and their growth rates are significantly different. Therefore the Tc dependence of crystallization behavior observed by POM is qualitatively similar to that obtained by SR-SAXS, though ξ is moderately different between both cases.