Crystallization Behavior and Crystal Orientation of Poly(ε-caprolactone) Homopolymers Confined in Nanocylinders: Effects of Nanocylinder Dimension

The crystallization behavior and crystal orientation of poly­(ε-caprolactone) (PCL) homopolymers and PCL blocks spatially confined in identical nanocylinders have been investigated using differential scanning calorimetry (DSC) and two-dimensional wide-angle X-ray diffraction (WAXD) as a function of cylinder diameter <i>D</i>. The PCL homopolymers confined in nanocylinders were prepared using microphase separation of PCL-<i>block</i>-polystyrene (PCL-<i>b</i>-PS) copolymers with a photocleavable <i>o</i>-nitrobenzyl group (ONB) between PCL and PS blocks and the subsequent cleavage of ONB by irradiating UV light. The time evolution of PCL crystallinity χ_PCL showed a first-order kinetics for both PCL blocks and PCL homopolymers confined in all the nanocylinders investigated. However, the <i>D</i> dependence of crystallization rates for PCL blocks was more drastic than that for PCL homopolymers, and consequently various <i>D</i>-dependent interrelations were observed between crystallization rates of PCL blocks and PCL homopolymers. The crystal orientation was also dependent on <i>D</i>; the <i>b</i>-axis of PCL crystals oriented parallel to the cylinder axis both for PCL blocks and PCL homopolymers confined in the nanocylinder with <i>D</i> = 13.0 nm, whereas the (110) plane of PCL crystals was normal to the cylinder axis in the nanocylinders with <i>D</i> ≥ 14.9 nm. The difference in the degree of crystal orientation was not detected between PCL blocks and PCL homopolymers confined in nanocylinders with <i>D</i> ≥ 14.9 nm