Crystallization of double crystalline block copolymer/crystalline homopolymer blends: 2. crystallization behavior

We examined the isothermal crystallization behavior of poly(ɛ-caprolactone) (PCL) chains (that is, PCL blocks and PCL homopolymers) in binary blends consisting of PCL-block-polyethylene (PCL-b-PE) copolymers and PCL homopolymers using simultaneous synchrotron small-angle X-ray scattering/wide-angle X-ray diffraction (SAXS/WAXD) and independently using Fourier transform infrared spectroscopy (FTIR). Because the crystallizable temperature of PE blocks was significantly higher than that of PCL chains, the PE block crystallized first upon quenching to form a crystalline lamellar morphology (PE lamellar morphology) and subsequently the PCL chain crystallized within this morphology. We prepared two blends by considering the miscibility of PCL homopolymers in microphase-separated melts; when the PCL homopolymer was localized between PCL blocks in the lamellar microdomain (dry brush), the crystallinity of PCL chains showed a composition-dependent asymptotic increase at the late stage of crystallization, suggesting the individual crystallization of PCL homopolymers and PCL blocks to yield separate PCL lamellar crystals in the PE lamellar morphology. When the PCL homopolymer was uniformly mixed with PCL blocks (wet brush), the time evolution of crystallinity was identical to that of PCL blocks irrespective of composition, indicating that the crystallization of PCL chains was virtually controlled by that of PCL blocks to form a mixed crystal of PCL blocks and PCL homopolymers.