Poly(ionic liquid)-Based Covalently Adaptable Networks (PIL-CANs): Polar and Dipolar Interactions

This Letter outlines the synthesis of imidazolium (Im⁺)-(bis((trifluoromethyl) sulfonyl)amide) (TFSI^-)-based poly(ionic liquid)-based covalently adaptable networks (PIL-CAN) containing variable length aliphatic spacers terminated with acetoacetate (AcAc) and cross-linked by tris(2-aminoethyl) amine (TREN). These PIL-CANs exhibit the storage modulus in the order of ∼2.5-3.0 GPa and can undergo multiple reprocessing by mechanical damage and compression molding at 120 °C. The recovery of physical and chemical properties involves exchange reactions between imine and enamine, and keto and enol tautomers. Upon reprocessing, storage moduli, junction densities, and entropic energy are preserved. These thermally stable CAN-PILs exhibit storage modulus values comparable to those of high-performance phenolic or epoxy networks but significantly lower glass transition temperatures (T_g). While storage moduli and junction densities in the glassy region are functions of molecular weight and aliphatic spacer length, the entropy remains unchanged due to polar and dipolar contributions. If backbone and side chains are "locked" in place, no structural changes will occur to enable configurational changes, and the thermal motion and/or the free volume will dominate entropy rather than the backbone structure.