Novel cholesteric liquid crystalline elastomers containing dimer type nematic and chiral liquid crystalline side-chains

摘要

A new set of cholesteric side chain liquid crystalline elastomers (ChLCEs) E _(1) –E _(7) were graft copolymerized by hydrosilylation reaction with poly(methylhydrogeno)siloxane, nematic monomer (M _(1) ), chiral monomer (M _(2) ), and crosslinking agent (CL). The two monomers were both dimers, and the chiral 2-octyl terminal group was firstly used in the ChLCE systems. The chemical structures of M _(1) , M _(2) and CL were carefully examined by Fourier transform infrared (FT-IR), elemental analysis (EA), proton nuclear magnetic resonance spectroscopy ( ~(1) H NMR); and their mesomorphic phases were determined by observation using polarizing optical microscopy (POM), and double confirmed by calculations from the results of X-ray diffraction (XRD). The helical structure of combining the chiral and achiral liquid crystalline side chains endowed the obtained ChLCEs with cholesteric liquid crystalline properties. By tailoring the dosage of the crosslinking agent, the mesomorphic properties of ChLCEs could be adjusted. The mesophase-isotropic phase ranges of the ChLCEs were gradually narrowed with the increasing addition of CL according to differential scanning calorimetry (DSC). Thermal analysis (TG) results showed the temperatures at which 5% weight loss occurred were greater than 300 °C for all the ChLCEs. The effective crosslink density ( _(c) ) of the ChLCEs was characterized by swelling experiments showing that the molecular weight between the crosslinking points decreases with the increase of the CL. Fourier transform infrared imaging (FT-IR imaging) and FT-IR indicate the functional groups of all the ChLCEs are finely distributed.