High-Performance Polyethylene-Ionomer-Based Thermoplastic Elastomers Exhibiting Counteranion-Mediated Mechanical Properties

Because of their superior mechanical properties, excellent processability, reusability, and recyclability, thermoplastic elastomers (TPEs) have attracted considerable research attention. For random polyolefin-based TPEs, because the high crystallinity contributes to the high strength while decreasing the elastic recovery, the management of the tradeoff between the strength and stretchability is a critical challenge. Therefore, in this study, an elastomer was prepared based on a dual-cross-linking strategy by combining physical cross-links originating from polyolefin crystallinity and dynamic ionic cross-linking to resolve the tradeoff between the tensile strength and elastic recovery. First, ethylene/5-iodomethyl-2-norbornene/1-hexene terpolymers were synthesized with reactive iodine atoms, and the active sites were then transformed into a series of imidazolium-based ionomers bearing methane sulfonate (CH3SO3–), trifluoromethanesulfonate (CF3SO3–), or bis(trifluoromethane)sulfonimide (Tf2N–) counteranions via ionization and ion exchange. The interaction intensities between counteranions and imidazolium ions varied depending on the counteranion type. The ionomers containing CH3SO3– showed the highest tensile strength of up to 13.7 MPa, and those containing Tf2N– presented a favorable strain-at-break of up to 624%. The tensile properties were modulated over a broad range by changing the counteranion type and content. Moreover, because cross-links were generated by both ionic interactions and polyethylene crystallinity, the ionomers displayed excellent elastic recovery of up to 96%.