Polysiloxane-Based Liquid Crystalline Polymers and Elastomers Prepared by Thiol-Ene Chemistry

A series of side-chain liquid crystalline polymers (LCPs) with polysiloxane backbones have been synthesized by grafting mesogenic monomers to poly[3-mercaptopropylmethylsiloxane (PMMS) via thiol-ene click chemistry. Their properties were studied in detail by a combination of H-1 NMR, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy and small angle X-ray scattering. In comparison with the traditional hydrosilylation method which requires noble metal catalyst platinum, this newly designed thiol-ene protocol produces polysiloxane-based LCPs with only anti-Markovnikov addition products under benign conditions Moreover, by controlling the molar ratio of PMMS and mesogenic monomers, PMMS-based LCPs can be partially functionalized, meanwhile leaving spare mercapto groups, which could be further used as cross linking sites to prepare polysiloxane-based liquid crystalline elastomers (LCEs). Besides preparing LCE fibers with a maximum contraction of 42% at nematic-to-isotropic transition temperature, we further explored the feasibility, of using surface-rubbed cells to synthesize LCE films, but it turned out that this method could uniaxially align the mesogens of preformed short polymers but not the backbone chains so that the thermal-actuation effects of these films were modest.