(540a) Liquid Crystal Elastomer Network Structure and Phase Behavior

Liquid crystal elastomers (LCEs) are crosslinked polymer networks that can undergo a phase transition between the disordered isotropic state and the ordered liquid crystalline state in response to external stimuli. Due to the coupling of polymer chain anisotropy and liquid crystalline order, liquid crystal elastomers exhibit remarkable properties from programmable shape morphing, to soft elasticity (in which large deformations can be achieve at nearly zero stress), and mechanotropic behavior, in which the phase transition is induced by an applied strain. However, while small molecule liquid crystals and liquid crystalline polymers often exhibit a nearly first order phase transition, liquid crystal elastomers exhibit a continuous phase transition that has been attributed to the effects of quenched random disorder. Here, we examine the role of liquid crystal elastomer network structure on its phase behavior, in particular focused on investigating controlled model networks with reduced heterogeneity relative to conventional main-chain liquid crystal elastomers. We demonstrate the synthesis of main-chain monodisperse liquid crystalline polymers via both an iterative exponential growth approach from custom monomers as well as the fractionation of conventional liquid crystalline polymers, and investigate the thermotropic phase behavior of these precise polymers in both linear and networked form. In addition, we probe the relative role of small molecule crosslinker concentration versus crosslink density on the phase transition temperature and breadth.