Photoresponsive side-chain liquid crystalline polymers with an easily cross-linkable azobenzene mesogen

The synthesis of a series of novel photoresponsive side-chain liquid crystalline polymers (LCPs) bearing an N-hydroxysuccinimide carboxylate-substituted azobenzene mesogen and their use in generating LCP networks are described. The obtained polymers and their monomers were characterized with H-1 NMR, UV-vis, TGA, DSC, POM and SAXS techniques. The length of the flexible spacers in the polymers and their monomers show significant influence on their properties such as the phase transition behaviors and the monomer reactivity. The polymerization reactivity of the monomers increases with an increase in the spacer length and only those monomers and polymers with a flexible spacer >= (CH2)(6) show liquid crystallinity with their mesophases being smectic A. In addition, the polymers have proven to be easily cross-linkable with a difunctional primary amine under mild conditions both in solution and in film, demonstrating that they are very useful precursors for photoresponsive LCP networks. Furthermore, the photoresponsivity of the polymer solution in tetrahydrofuran and the crosslinked polymer film was also confirmed by their occurrence of the UV and visible light-induced trans/cis photoisomerization.