Synthesis of Reactive Azobenzene Main-Chain Liquid Crystalline Polymers via Michael Addition Polymerization and Photomechanical Effects of Their Supramolecular Hydrogen-Bonded Fibers

A new and efficient strategy for obtaining a series of reactive azobenzene (azo)-containing main-chain liquid crystalline polymers (LCPs) is described, which involves the first design and synthesis of acrylate-type azo monomers with different length of flexible spacers and an amino end-group (in its trifluoroacetate salt form) and their subsequent Michael addition polymerization under mild reaction conditions. The resulting polymers showed rather high thermal stability, relatively low glass transition temperatures, a broad temperature range of smectic C liquid crystalline phase, and reversible photoresponsive behavior. The presence of secondary amino groups in the backbones of these azo main-chain LCPs not only made them highly reactive precursors for various new functional linear and cross-linked azo LCPs but also led to the formation of hydrogen-bonding interactions among their polymer chains. Supramolecular hydrogen-bonding cross-linked LCP fibers were directly fabricated by using the simple melt spinning method, which proved to have a high order of mesogen along the fiber axis and exhibit good mechanical properties, fast and reversible photoinduced bending and unbending behaviors, and large photoinduced stress (240 kPa) at close to ambient temperature as well as excellent photodeformation fatigue resistance.