Ionic crosslinked polypropylene-based thermoplastic elastomers with excellent mechanical properties

Abstract

Polyolefin thermoplastic elastomers (PO-TPEs) with excellent mechanical properties and processability have caused wide public concern over recent years. In this paper, we report ionic crosslinked polypropylene-based thermoplastic elastomers, which exhibited excellent toughness and elastic recovery. First, propylene/11-iodine-1-undecene/1-eicosene terpolymers were synthesized with a dimethyl(pyridyl-amido)hafnium caatalyst, and then, iodine atoms were converted into ionic groups via a nucleophilic substitution reaction with N-methylimidazole. This was followed by transforming them into imidazolium-based ionomers bearing different counteranions including bis(trifluoromethane)-sulfonimide (Tf₂N⁻), trifluoro-methanesulfonate (CF₃SO₃⁻), and methanesulfonate (CH₃SO₃⁻) via ion exchange. The introduction of the ionic groups led to a significant enhancement of tensile strength for ionomers. Moreover, the breaking strength and breaking elongation of materials can be adjusted over a wide range by changing the type of the counteranions. Benefiting from the dual crosslinks of the propylene crystallinity and ionic interaction, the ionomer with CH₃SO₃⁻ enjoyed a superior tensile strength (26.3 MPa), a preferable elongation at break (1225%) and favorable elastic recovery (70%). The excellent mechanical properties of the polypropylene-based elastomers offer great potential in areas such as auto parts, food packaging, and biomedical equipment.