Hyperbranched Polyethylene lonomers Containing Cationic Tetralkylammonium Ions Synthesized by Pd-Diimine-Catalyzed Direct Ethylene Copolymerization with Ionic Liquid Comonomers

Synthesis of polyolefin-based ionomers through direct catalytic copolymerization of olefin with ionic comonomers has been challenging with no prior reports. We demonstrate in this article the first direct synthesis of a class of hyperbranched polyethylene ionomers containing positively charged tetralkylammonium ions and different counteranions (tetrafluoroborate, hexafluorophosphate, bis-(trifluoromethane)sulfonimide, or hexafluoroantimonate) by copolymerization of ethylene with tetralkylammonium-containing acrylate-type ionic liquid comonomers (3-5, 7). The use of a Pd-diimine catalyst (1), which shows excellent stability toward the highly polar ionic group, is key to the direct synthesis. A detailed study on the catalytic copolymerization and the effects of the polymerization condition on the macromolecular chain parameters of the resulting ionomers has been performed. A range of ionomers differing in ion content and counteranion has been synthesized and characterized. Meanwhile, systematic studies on the structural, thermal, and melt rheological properties of the ionomers have been undertaken. The dramatic effects of ion incorporation on these properties, particularly on the rheological properties, are demonstrated.