Fixation of multilayered structures of liquid-crystalline 2:1 complexes of benzoic acid derivatives and dipyridyl compounds and the effect of nanopillars on removal of the dipyridyl molecules from the polymers

A polymerizable benzoic acid derivative, 3,5-bis(propenoyloxymethyl)-4- hexadecyloxybenzoic acid (1), was synthesized and complexed in a molar ratio of 2:1 with each of the dipyridyl compounds 4,4 '-bipyridyl (2a), 1,2-dipyridylethane (2b), 1,2-dipyridylethene (2c), and 1,3-dipyridylpropane (2d). All of these 2:1 complexes exhibited a monotropic smectic A liquid crystal phase. Complex compound 1(2)center dot 2b (denoted 3b) in the liquid crystal phase was photopolymerized by UV irradiation. As the polymerization proceeded, the multilayered structure of 3b was maintained. In addition, the polymerizations of 3b containing the polymerizable rodlike compound PL at concentrations of 5 and 10 mol % also proceeded in the smectic A phases while maintaining their multilayered structures. By treatment with dilute hydrochloric acid for 216 h, all of the 2b molecules were removed from the polymer obtained from a Mixture of 3b and PL in a molar ratio of 90: 10, though only 50% of 2b could be removed from the polymer obtained from pure 3b. This suggested that PL molecules cross-linked each pair of polymer sheets and functioned as nanopillars between the two sheets.