Synthesis, structures, and properties of side-chain cholesteric liquid-crystalline polysiloxanes

The synthesis of three cholesteric monomers and side-chain liquid-crystalline polymers was described. The structure-property relationships of monomers IM-IIIM and polymers IP-IIIP were discussed. Their phase behavior and optical properties were investigated by differential scanning calorimetry, thermogravimetric analyses (TGA), and polarizing optical microscopy. Monomers IM-IIIM exhibited cholesteric oily-streak texture and focal-conic texture. Polymers IIP and HIP revealed smectic A fan-shaped texture and cholesteric grandjean texture, respectively. Experimental results demonstrated that the selective reflection of IM-IIIM shifted to the short-wavelength region with increasing the flexible spacer length or decreasing the rigidity of the mesogen. Polymers with a longer flexible spacer had lower glass-transition temperatures and wider mesomorphic temperature ranges. TGA showed that the temperatures at which 5% weight loss occurred were greater than 300degreesC for all the polymers. (C) 2003 Wiley Periodicals, Inc.