Synthesis and mesomorphic properties of side-chain cholesteric liquid-crystalline polysiloxanes

A series of new side-chain cholesteric liquid-crystalline polysiloxanes was synthesized by grafting copolymerization. The chemical structures of the obtained monomers and polymers were confirmed by Fourier transform infrared or 1H-NMR spectroscopy. The mesomorphic properties were investigated with differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the content of cholesteryl 4-allyloxybenzoate on the phase behavior of the polymers was examined. The monomer 4-(undec-10-en-1-yloxy)-4ʹ-(4-ethoxybenzoyloxy)biphenyl showed nematic and smectic (A, C, and B) phases upon cooling, and cholesteryl 4-allyloxybenzoate revealed an enantiotropic cholesteric phase. One polymer showed a nematic schlieren texture, other polymers showed cholesteric Grandjean and oilystreak textures, and another polymer showed a smectic fan-shaped texture. The experimental results demonstrated that the glass-transition temperature and clearing temperature decreased first and then increased with an increasing content of cholesteryl 4-allyloxybenzoate.