Inverse Vulcanization of Vinyl-polycyclic Aromatic Hydrocarbon Monomers and Dynamic Covalent Polymerization with Liquid Crystalline Monomers

Recently, sulfur polymers have attracted great attention due to their self-healing ability and shape memory behavior. In this work, we report the effect of pendant ring structures on the thermomechanical and shape memory behavior of liquid-crystalline sulfur terpolymers. Copolymers were prepared via inverse vulcanization from various vinyl-polycyclic aromatic hydrocarbon (PAH) monomers, and the sulfur-PAH copolymers were subsequently reacted with the liquid crystal monomer (RM257) to prepare cross-linked terpolymers. The PAH monomers with various pendant groups reacted similarly to styrene and the glass transition temperature (Tg) increased as the number of fused rings in the pendant group increased. The LC-sulfur terpolymers could be thermally healed and reprocessed above the dynamic temperature due to the dynamic sulfur–sulfur bonding in the polymer. Two types of shape memory behavior are demonstrated: (i) a macroscopic folding and unfolding shape memory process and (ii) a microscopic optical surface grating shape memory process. Permanent shapes were prepared above the dynamic temperature, and temporary shapes were created between the Tg and the dynamic temperature and then fixed by lowering the temperature below the Tg. The stretched terpolymers containing liquid crystal components exhibited good birefringence, with a dichroic ratio of ∼1.36.