Preparation of a new polymer-dispersed liquid crystal film by using phthalocyanine-functional photocurable copolymer

A new, asymmetrical zinc phthalocyanine (aZnPc)-functional photocurable copolymer was prepared by the combination of atom transfer radical polymerization and copper (I)-catalyzed azide-alkyne cyclo-addition (CuAAC) click reaction and used as polymer matrix of polymer dispersed liquid crystal (PDLC) film. For this purpose, aZnPc was prepared through statistical condensation of 4-tert-butylphthalonitrile and 4-pent-4-ynyloxyphthalonitrile. Double CuAAC click reaction between azido-functional poly(methyl methacrylate-co-2-(2-bromoisobutyryloxy)-ethyl methacrylate), terminal alkynyl-substituted aZnPc, and 4-ethynyl-N,N-dimethyl aniline yielded photocurable aZnPc-functional copolymer. Thereby, synthesized copolymer was crosslinked in the presence of liquid crystalline mesogen 4′-(octyloxy)-4-biphenylcarbonitrile by ultraviolet irradiation using benzophenone as initiator and ethylene glycol dimethacrylate as difunctional crosslinker. Thermal and optical properties of PDLC film were investigated by using differential scanning calorimetry and polarized optical microscopy. Smectic A liquid crystal mesophases were observed in both PDLC film and its mesogenic component 4′-(octyloxy)-4-biphenylcarbonitrile.