Inverse Vulcanization\nof Vinyl-polycyclic Aromatic\nHydrocarbon Monomers and Dynamic Covalent Polymerization with Liquid\nCrystalline Monomers

Recently, sulfur polymers have attracted great attention\ndue to\ntheir self-healing ability and shape memory behavior. In this work,\nwe report the effect of pendant ring structures on the thermomechanical\nand shape memory behavior of liquid-crystalline sulfur terpolymers.\nCopolymers were prepared via inverse vulcanization from various vinyl-polycyclic\naromatic hydrocarbon (PAH) monomers, and the sulfur-PAH copolymers\nwere subsequently reacted with the liquid crystal monomer (RM257)\nto prepare cross-linked terpolymers. The PAH monomers with various\npendant groups reacted similarly to styrene and the glass transition\ntemperature (<i>T</i><sub>g</sub>) increased as the number\nof fused rings in the pendant group increased. The LC-sulfur terpolymers\ncould be thermally healed and reprocessed above the dynamic temperature\ndue to the dynamic sulfur–sulfur bonding in the polymer. Two\ntypes of shape memory behavior are demonstrated: (i) a macroscopic\nfolding and unfolding shape memory process and (ii) a microscopic\noptical surface grating shape memory process. Permanent shapes were\nprepared above the dynamic temperature, and temporary shapes were\ncreated between the <i>T</i><sub>g</sub> and the dynamic\ntemperature and then fixed by lowering the temperature below the <i>T</i><sub>g</sub>. The stretched terpolymers containing liquid\ncrystal components exhibited good birefringence, with a dichroic ratio\nof ∼1.36.