Mechanochemical Route to Graphene-Supported Iron Catalysts for Olefin Polymerization and in Situ Formation of Carbon/Polyolefin Nanocomposites

A facile one-step mechanochemical process converts graphite into highly active graphene-supported iron catalysts for ethylene polymerization and the in situ formation of graphene/polyethylene nanocomposites. Key feature is the dry grinding of graphite in a steel ball mill under carbon dioxide pressure, affording high surface area edge-carboxylated graphene accompanied by simultaneous immobilization of Fe2+, formed by iron abrasion and electron transfer reaction. In contrast, as evidenced by Mossbauer spectroscopy, grinding graphite in the absence of carbon dioxide under nitrogen or argon pressure produces predominantly Fe degrees together with Fe3+ supported on nitrogen-functionalized graphene or micronized graphite, respectively. On addition of bisiminopyridine (BIP) and activation with methylaluminoxane (MAO), only the Fe2+ catalyst supported on edge-functionalized graphene (Fe@MG-CO2) polymerizes ethylene in high yields, producing polyethylene with a molar mass of 180 kg/mol and a polydispersity of 6.1. According to the transmission electron microscopic analysis of polyethylene morphology, functionalized graphene with low aspect ratio is uniformly dispersed in the polyethylene matrix. Hence, this mechanochemical catalyst preparation enables the fabrication of graphene/polyolefin nanocomposites with high carbon content by polymerization filling using cost-effective graphite as raw material without requiring tedious and expensive graphite functionalization in separate steps.