Crystal Orientation of Poly(ε-caprolactone) Homopolymers Confined in Cylindrical Nanodomains

Abstract

The crystal orientation of poly(ε-caprolactone) (PCL) homopolymers, spatially confined in cylindrical nanodomains surrounded by polystyrene (PS) matrices, has been investigated as a function of crystallization temperature Tc (−60 °C ≤ Tc ≤ −40 °C) using two-dimensional small-angle X-ray scattering (2D-SAXS) and wide-angle X-ray diffraction (2D-WAXD). The sample was prepared by microphase separation of an PCL-block-PS copolymer followed by photocleavage at the block junction between PCL and PS blocks. The results were compared with crystal orientation of PCL blocks before photocleavage, i.e., PCL chains with one chain-end tethered at the cylinder interface. The lamellar crystals of PCL homopolymers and PCL blocks were preferentially oriented in cylindrical nanodomains irrespective of Tc, i.e., the b axis of crystal unit cells was oriented parallel to the long axis of cylinders. The degree of crystal orientation increased remarkably with increasing Tc for PCL homopolymers, whereas it improved slightly for PCL blocks, yielding a large difference in the degree of crystal orientation between two systems at higher Tc (≥−45 °C).