Spatial anisotropy in poly(vinylcinnamate) films

A null ellipsometry technique is applied to the study of spatial structural properties of poly (vinylcinnamate) (PVCN) and poly(vinyl E-4-fiuorocinnamate) (PVCN-F) films before and after irradiation with actinic UV light. Based on the results, three-dimensional (3D) orientational configurations of cinnamoyl fragments are estimated. The orientation of cinnamoyl groups in original PVCN films is spatially isotropic, while in PVCN-F films a slight preference for the out-of-plane alignment is detected. Both uniaxial and biaxial structures were induced by polarized UV light depending on material and irradiation conditions. In the irradiated films the refractive index reaches its minimum along the direction of polarization of the actinic UV light E and maximum in the directions perpendicular to E. This indicates effective crosslinking of cinnamate groups along the direction of light polarization and preferential orientation of the remaining cinnamate fragments in the directions perpendicular to E. Under certain irradiation conditions for PVCN-F and under all irradiation conditions for PVCN the remaining cinnamoyl fragments are distributed randomly in the plane perpendicular to E. The result is a negative A-plate with the optic axis along the polarization direction. The polymer films irradiated with nonpolarized light have refractive properties typical of uniaxial plates with positive birefringence (positive C and O plates). The optic axis of these films is determined by the direction of light propagation and corresponds to preferential orientation of the cinnamoyl fragments. The obtained films may be used for compensation of liquid crystal displays and improvement of their optical characteristics.