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(epsilon-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 T-c. The characteristic size of the phase-separated structure xi existing in this blend before crystallization can arbitrarily be controlled by changing the phase separation time. When the blend with xi = 2.5 mu m is quenched into various T-c, 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 T, (<= 35 degrees C), while they deviate gradually with increasing T-c. Only one type of spherulites is observed for the blend with = 10 mu m crystallized at T-c = 35 degrees C to give a single growth rate, while two different types of spherulites appear at higher T, (>= 40 degrees C) and their growth rates are significantly different. Therefore the T-c dependence of crystallization behavior observed by POM is qualitatively similar to that obtained by SR-SAXS, though is moderately different between both cases.