Unveiling the role of base catalysts in the thiol-Michael addition reaction in liquid crystal oligomers and liquid crystal elastomers.

Liquid crystal oligomers (LCOs) and liquid crystal elastomers (LCEs) are currently receiving much attention as stimuli-responsive polymer materials capable of adapting to environmental changes such as light and temperature, resulting in changes in functional properties including shape and colour. The base-catalysed thiol-Michael addition is widely used to synthesize LCOs and LCEs, yet the role of the catalyst is often overlooked. This study shows that commonly used amine catalysts form base adducts with the liquid crystal building blocks. In the case of triethylamine, this side reaction is avoided, enabling a 95% acrylate conversion in the thiol-Michael addition reaction used to synthesize LCOs. Thermomechanical analyses of the corresponding LCEs demonstrate that the materials free from nucleophilic base adducts and with a high thiol-Michael addition reaction conversion exhibit an increased Young's modulus and enhanced stiffness and stress resistance, which is likely attributable to a higher crosslink density. Our work provides guidelines for the synthesis of liquid crystal oligomers and elastomers, potentially improving the performance of stimuli-responsive materials and devices.