Side-Chain Cholesteric Liquid Crystalline Elastomers Derived from a Mesogenic Cross-Linking Agent

The synthesis of the two monomers M 1 and M 2 and a series of new side-chain cholesteric liquid crystalline elastomers P 2 − P 8 is presented. The chemical structures of the monomers and elastomers obtained were confirmed by FTIR or 1 H NMR spectroscopy. The cross-link density of the elastomers was determined by swelling experiments. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. Monomer M 1 showed a cholesteric phase, and M 2 revealed smectic and nematic phases. The effect of the cross-link density on the phase behavior of P 2 − P 8 is discussed. Elastomers P 2 − P 6 containing less than 12 mol % of the cross-linking units displayed elasticity, reversible liquid crystalline phase transition, wide mesophase temperature ranges, and high thermal stability. Elastomer P 7 displayed stress-induced birefringence, and P 8 showed only elasticity with no other texture. Experimental results demonstrated that the glass transition temperatures increased, and the isotropization temperatures and the mesophase temperature ranges of P 2 − P 6 decreased with increasing cross-link density.