Orange is the new white: Rapid curing of an ethylene-glycidyl methacrylate copolymer with a Ti-bisphenolate type catalyst
Journal article, 2018
Polyethylene must be crosslinked if the polymer is to be used at elevated temperatures. However, established crosslinking methods result in the release of volatile by-products that can compromise the cleanliness and purity required for many electrical and medical applications. Currently available alternative curing processes, free from by-product formation, are too slow to be of practical relevance. Here, we demonstrate that an epoxy-bearing polyethylene copolymer, which contains one glycidyl methacrylate comonomer per 64 ethylene monomers, can be rapidly crosslinked with a click-chemistry curing process. We show that a titanium-based Lewis acid together with a bisphenol crosslinking agent allows the formation of thermosets. Compounding of the Lewis acid catalyst, crosslinking agent and copolymer through extrusion at 140 °C can be carried out without onset of the curing reaction. Then, at more elevated temperatures of 180 °C and above rapid crosslinking occurs. The competitive curing rate of the here explored formulation is due to in situ generation of a new titanium-phenoxide catalyst, which efficiently promotes crosslinking of the epoxy-bearing polyethylene copolymer. Adjustment of the curing time and temperature results in a high network density of at least 3 crosslinks per 1000 carbons in only 2 minutes at 240 °C and at a curing agent stoichiometry of 3 wt%, which corresponds to merely 0.04 wt% elemental titanium. The here established crosslinking chemistry opens up a by-product free method for rapid curing of epoxy-functionalised polyethylenes.