Transesterification in Epoxy-Thiol Exchangeable Liquid Crystalline Elastomers

The incorporation of vitrimer bond-exchange chemistry into liquid crystalline elastomer networks produces "exchangeable liquid crystal elastomers" (xLCE). These materials offer a facile method of material reshaping and alignment postpolymerization via the application of a mechanical stress above the temperature of activation of bond exchange. We use diepoxy mesogenic monomers with thiol-terminated spacers and crosslinker to investigate a range of resulting xLCE. The "click" chemistry of thiols results in good control over the network topology and low glass transition in this family of materials. By combining different spacers, we were able to obtain smectic and nematic phases and adjust the liquid crystal to the isotropic phase transition between 42 and 140 degrees C, while the elastic-plastic transition temperature was maintained close to 200 degrees C. The broad gap between these temperatures ensures that thermally actuating uniformly aligned elastomers are stable and show no residual plastic creep, making epoxy-thiol xLCE promising for a range of engineering applications.