Systematic Investigation of Liquid Crystalline Elastomers Prepared by Thiol–Ene Photopolymerization

Abstract

Liquid crystalline elastomers (LCEs) prepared via thiol–ene photopolymerization result in homogeneous distribution of molecular weight between cross-links. Numerous prior reports emphasize that LCEs are material actuators that undergo a thermomechanical response associated with an order–disorder transition. However, modern and widely utilized approaches to create LCEs result in heterogeneous networks. Theoretical examination suggests that network heterogeneity and high degrees of cross-linking cause a continuous association of strain with temperature, rather than a first-order, stepwise association. Alternatively, thiol–ene photopolymerization historically yields homogeneous polymers with tailorable cross-link densities. This report extends these prior studies to formulations, which are conducive to LCE preparation. Specifically, this examination copolymerizes a liquid crystalline dialkene mesogen with a tetrathiol cross-linker and dithiol chain extender via a purely thiol–ene polymerization. Notably, this composition is amenable to surface-enforced alignment. This contribution exploits the tunability of thiol–ene photopolymerization to emphasize the influence of cross-linking on the coupling of strain and temperature.