Photoinduced molecular reorientation in photoreactive liquid crystalline copolymers in a phase retarder application

Polymethacrylate copolymers, which have hexamethylene spacer groups terminated with 4-methoxyphenyl-4′-oxycinnamate (MPC) and 4-oxybenzoic acid (BA) in the side chain, were synthesized. Thin films underwent thermally enhanced photoinduced cooperative molecular reorientation using linearly polarized ultraviolet (LPUV) light and subsequent annealing. Moreover, low exposure energy (4-80 mJ cm⁻²) and annealing temperature (<140 °C) provided sufficient cooperative molecular reorientation of both side groups with a large reorientational order (S > 0.5). Tuning the copolymer composition adjusted the birefringence (?n) of homogeneously reoriented films between 0.10 and 0.22 at 517 nm. Finally, a phase retarder (?nd = 130 nm) using an oriented copolymer on a triacetylcellulose (TAC) film substrate, which exhibited a thermal stability up to 140 °C, was fabricated.