Trapping crystallinity in highly crosslinked thermosets by light-based 3D printing from the liquid crystalline phase

Abstract

We propel photopolymerizable liquid crystalline (LC) shape memory materials from solely elastomeric performance to the thermomechanical performance of tough, yielding thermosets. LC elastomers are at the forefront of smart, stimuli-responsive materials development. To apply their properties to mechanically superior thermosets, we demonstrate main-chain incorporation of high quantities of preordered LC motifs into a densely crosslinked network via thiol-ene photopolymerization to achieve a new material class hybridizing the advantages of LC elastomers and liquid crystalline networks. A terminal alkene mesogen with a robust LC phase is combined with multiple trithiol comonomers and selected based on resulting polymer crystallinities (13-37%). The bulk materials exhibit high strength, stiffness and pronounced yielding under stress with elongations around 200%. Their excellent thermomechanical properties were explained by phase separation observed in atomic force microscopy. Furthermore, we demonstrate shape memory of these materials with fast, near-perfect shape imprinting (99%) and recovery (97%) over at least 20 cycles, and their light-based 3D printing at high temperature.