Polymer Network Structure, Properties, and Formation of Liquid Crystalline Elastomers Prepared via Thiol-Acrylate Chain Transfer Reactions

Liquid crystalline elastomers (LCEs) are functional materials whose stimuli response is strongly influenced by the composition and structure of the polymer network. LCEs are commonly fabricated by copolymerizing acrylate monomers with thiols. This work explores the formation of LCE polymer networks via photopolymerization reactions of diacrylate liquid crystalline monomers with dithiols. Detailed analysis of model systems based on monoacrylate-dithiol reactions indicates that the polymer network architecture of LCEs prepared by this reaction contains extensive unreacted thiol content as dangling ends. Further, kinetic analysis indicates that polymerization in a liquid crystalline phase strongly hinders the mobility of reactive species during the formation of the LCE polymer network, which is evident in the substantial difference in viscosity between liquid crystalline monomers (0.0195 Pa s) and non-liquid crystalline monomers (0.0025 Pa s). In copolymerization with the diacrylate liquid crystal monomers, the dithiol comonomer significantly decreases the elastic modulus and T-g. The residual thiol in the LCE polymer network can be postfunctionalized with reactive additives.