Liquid Crystalline Elastomers Prepared by Catalytic Chain Transfer Photopolymerization of Methacrylate Liquid Crystal Monomers

Liquid-crystalline elastomers (LCEs) are soft, anisotropic materials exhibiting stimuli-responsive properties with potential utility in robotics, optics, and sensing. Historically, LCEs have been prepared via hydrosilylation reactions to form polysiloxane materials with either main-chain or side-chain liquid crystalline segments. Many recent examinations of LCEs utilize more accessible synthetic methods based on photopolymerization of acrylated monomers and compositions that contain heteroatom chain transfer or chain extension agents (e.g., thiols or amines) to enable network formation and alignment control. Here, we report the preparation of heteroatom-free (Si, S, and N) LCEs composed almost entirely of liquid crystalline precursors via catalytic chain transfer photopolymerization. Incorporation of a macrocyclic cobaloxime catalyst (CoBF) into formulations nearly entirely composed of a methacrylate liquid-crystal monomer (MeC6M) enables precise tuning of network mechanics and stimuli-responsive behavior through controlled chain transfer. The LCE maintains properties and stimuli response comparable to LCEs prepared by previously established methods with catalyst loading providing a direct handle over network mechanics and thermomechanical actuation.