New Optical Response Of The Synthesis And Properties Of Side-chain Liquid Crystal Polymer And Polymer Network

The photoresponsive properties of the azobenzene (azo) polymers are based on the photoinduced fast and reversible isomerization between the trans and cis isomers of azobenzene upon exposure to UV or visible light, which triggers significant changes in the physicochemical properties of polymer materials. Recent years have witnessed a rapidly increasing interest in azo-containing polymers due to their potential in various optical and optoelectronic applications such as optical data storage, liquid-crystal displays, molecular switches, nonlinear optical devices, photomechanical systems and so on.Aiming at preparing new photoresponsive side-chain liquid crystalline polymers and crosslinked liquid crystalline polymer networks, we synthesized two series of the side chain liquid crystalline polymers containing either an easily cross-linkable azobenzene mesogen or amide-substituted azo mesogen, and studied in detail their liquid crystalline behaviors and photochromic properties. The dissertation presents the following main points:1. A series of novel photoresponsive side-chain liquid crystalline monomers bearing an N-hydroxysuccinimide carboxylate-substituted azobenzene mesogen and their corresponding homopolymers have been synthesized. The obtained polymers and their monomers were characterized with ¹H NMR, UV-vis, TGA, DSC, POM and SAXS techniques. The length of the flexible spacers in the polymers and their monomers shows 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 crystalline 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.2. Design and synthesis of a series of novel photoresponsive side-chain liquid crystalline polymethacrylates bearing an amide-substituted azo mesogen with different spacer and tail length by free radical polymerization. The obtained polymers and their monomers were characterized with ¹H NMR, UV-Vis, TGA, DSC, POM and SAXS techniques. With the flexible spacer length increasing, the phase transition temperature decreased. And the phase transiton temperature changed disciplinary accordingly with the tail length being changed. The packing arrangements in their mesophases of the polymers were influenced by the end functional group obviously. All the polymers with amide-substituted group showed the partly interdigitated bilayer smectic phase structure. The polymer with ester-substituted group showed the single layer SA structure. Furthermore, the photoresponsivity of the polymer solution in tetrahydrofuran and the polymer film was also confirmed by their occurrence of the UV and visible light-induced trans/cis photoisomerization.