Synthesis And Properties Of Azobenzene Side-chain Liquid Crystalline Copolymer Containing Pendant POSS

Polyhedral oligomeric silsesquioxane (POSS) as a novel organic-inorganic hybrid has many potential applications in polymers/POSS composites due to its high thermal stability, flame retardation, and mechanical properties as well as low dielectric constant.The acrylic acid modified POSS (AC-POSS) has been synthesized by the reaction of POSS containing amine groups with acrylic acid. A free radical polymeraztion was applied to synthesize liquid crystalline polymers (LCP)/POSS copolymer (LCP-POSS) in the presence of AC-POSS and liquid crystalline monomers using AIBN as an initiator. And the chemical structures of the above products were confirmed by FT-IR and NMR spectra. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing the UV-irradiation time, accompanied by a decrease in the absorbance. LCPs and LCP-POSS showed the first-order photoisomerization reaction. As compared with the LCPs, the photoisomerization rate constant of LCP-POSS decreases due to the incorporation of the POSS as rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increases with the content of POSS, and the size of liquid crystalline domain in LCP-POSS decrescs. As the POSS content in LCP-POSS further increases, the ordered structure of liquid crystalline phase is gradually destroyed, resulting in the final disappearance of LCPs'liquid crystllinity due to the rigidity of POSS.