Molecular Engineering of Photoactive Liquid Crystallione Polyester Epoxies Containing Benzylidene Moiety

A series of photoactive liquid crystalline polyester epoxies incorporating bisbenzylidene segments as photoactive mesogenic cores were synthesized by polyaddition of diepoxy monomers and terephthalic acid/trimesic acid. To investigate the influence of structural parameters such as, molecular architecture, structural rigidity of mesogenic unit and substituents on thermal, mesogenic, and photoactive properties, the bisbenzylidene segment was incorporated into one acyclic and two cycloalkanone units with two and four substituents, respectively in both linear and hyperbranched architectures. Degree of branching of hyperbranched polymers was found to be in the range of 0.49-0.62. All polymers exhibited nematic mesophase (nematic droplets). Photo induced (2 pi + 2 pi) cycloaddition reaction, upon exposure to light at 365 nm, was examined. Triter molecular photocycloaddition was confirmed by photoviscosity measurement of UV irradiated polymer solutions. Faster photo induced reactivity of polymers in hyperbranched architecture was observed when compared to linear structure. Acyclic units facilitated photocycloaddition, and five-membered ring showed higher photoactivity compared to six-membered ring. The steric hindrance caused by substituents decreased the photoactivity of polymers. Refractive index change was found to be in the range of 0.015-0.024. Substantial variation of refractive index indicates that these polymers could be used for optical recording. (C) 2008 Wiley Periodicals, Ine. J Polym Sci Part A: Polym Chem 46: 7637-7655, 2008