Influence of molecular structure on anisotropic photoinduced decompositionof polyimide molecules

We have investigated the anisotropic decomposition of polyimide molecules i nduced by irradiation of linearly polarized ultraviolet light (LPUVL). Thre e polyimides were examined: poly [4,4'-oxydiphenylene-pyromellitimide], pol y [4,4'-oxydiphenylene-1,2,3,4-butanetetracarboximide] and poly [4,4'-oxydi phenylene-1,2,3,4-cyclobutanetetracarboximide] (CBDA-ODA). Anisotropic deco mposition was monitored by measuring the polarized infrared absorption spec tra of similar to 10 nm thick films as a function of LPUVL exposure. Among the three polyimides, CBDA-ODA showed the largest anisotropy of decompositi on in the initial stage of LPUVL exposure. This result suggests that CBDA-O DA is a suitable polyimide material for photoinduced liquid crystal alignme nt based on photodecomposition reactions. The details of the LPUVL exposure dependence of the film anisotropy are discussed. (C) 2001 American Institu te of Physics.