Synthesis and characterization of a series of side chain chiral smectic liquid crystalline elastomers

A series of new chiral smectic liquid crystalline elastomers was prepared by graft polymerization of a nematic monomer with a chiral and non-mesogenic crosslinking agent, using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and H-1 NMR. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X-ray diffraction. Monomer M-1 showed a nematic phase during heating and cooling. Polymer P-0 exhibited a smectic B phase; elastomers P-1 - P-3 showed the smectic A phase, P-4 - P-6 showed a chiral smectic C(SmC*), and P-7 displayed stress-induced birefringence. Elastomers containing less than 15 mol% M-2 displayed elasticity, reversible phase transitions with wide mesophase temperature ranges, and high thermal stability. With increasing content of the crosslinking unit, glass transition temperatures first increased, then fell, then increased again; isotropization temperatures and mesophase temperature ranges steadily decreased.