Crystallization Morphology and Orientation of PCL Ultrathin Films in Binary Blends with Poly(vinyl chloride) and Poly(4-vinylphenol)

The crystalline morphology and orientation in ultrathin films of polycaprolactone (PCL) blended with poly(vinyl chloride) (PVC) and poly(4-vinylphenol) (PVPh), respectively, were investigated. In the PCL/PVPh blend, dendritic crystals with truncated lozenge morphology were observed, whereas the PCL/PVC blend exhibited seaweed-like crystals characterized by approximately six curved branches. Electron diffraction patterns demonstrate that in both blend systems the PCL chain stems are oriented perpendicularly to the film surface, with the a- and b-axes aligned parallel to the film plane. However, the PCL/PVPh blend exhibits significantly enhanced orientation ordering of both a- and b-axes compared with the PCL/PVC system. Grazing incidence reflection infrared spectroscopy analysis indicates that the PCL c-axis in the PCL/PVPh blend exhibits a higher degree of perpendicular orientation relative to the substrate surface compared with that in the PCL/PVC system. Fourier transform infrared spectroscopy reveals stronger intermolecular interactions between PCL and PVPh than those in PCL/PVC, which may account for the morphology and orientation difference of PCL crystallization in the two blends. This study demonstrates that intermolecular interactions serve as one of the crucial factors contributing to the diversity of crystalline morphology and structure of polymers in thin films.