Synthesis of well-defined easily crosslinkable azobenzene side-chain liquid crystalline polymers via reversible addition–fragmentation chain transfer polymerization and photomechanical properties of their post-crosslinked fibers

• Published in: European polymer journal Vol. 69; pp. 592 - 604
• Main Authors: Fang, Liangjing, Han, Guang, Zhang, Jiayang, Zhang, Hongtao, Zhang, Huiqi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-2015
• Subjects: Addition polymerization; Azo; Azo polymers; Azobenzene; Chain transfer; Crosslinking; Fibers; Monomers; Photomechanical properties; Photoresponsive; Polymerization; Post-crosslinking; Reversible addition–fragmentation chain transfer (RAFT) polymerization; Side-chain liquid crystalline polymers; Photoresponsive; Side-chain liquid crystalline polymers; Photomechanical properties; Reversible addition–fragmentation chain transfer (RAFT) polymerization; Post-crosslinking; Azobenzene
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2015.01.001

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•A versatile approach has been developed for fabricating photodeformable fibers.•Some crosslinkable azo side-chain liquid crystalline polymers have been prepared.•Uncrosslinked azo fibers were first fabricated and they were then post-crosslinked.•The post-crosslinked azo fibers show excellent photoinduced bending behaviors.•The crosslinking densities of the fibers influence their photomechanical behaviors.
The synthesis of a series of well-defined easily crosslinkable azobenzene (azo) side-chain liquid crystalline polyacrylates (including both homopolymers with an N-hydroxysuccinimide carboxylate-substituted azo mesogen and copolymers with both the above crosslinkable azo mesogen and a non-crosslinkable azo mesogen) via reversible addition–fragmentation chain transfer (RAFT) polymerization and photomechanical properties of their post-crosslinked fibers are described. The RAFT polymerizations of the azo monomers proved to be living and well-controlled, as revealed by their linear kinetic plots as well as the linear increase of the molecular weights of the azo polymers with monomer conversions and their low molar-mass dispersities (Đ⩽1.17). All the obtained azo polymers exhibited high thermal stability and relatively low glass transition temperatures, but only the azo homopolymers with longer flexible spacers and azo copolymers showed liquid crystallinity. In addition, the crosslinked azo polymer fibers with easily controlled diameters and high alignment order were obtained by the first fabrication of the uncrosslinked azo polymer fibers by the simple melt spinning method and their subsequent crosslinking with a difunctional primary amine under mild conditions. The contents of the crosslinkable azo mesogen in the polymers had significant influence on the photomechanical properties of their post-crosslinked fibers, and those with appropriate crosslinking densities could exhibit fast and reversible photoinduced bending and unbending behaviors and excellent photodeformation fatigue resistance even at close to room temperature.