Orange is the new white: rapid curing of an ethylene-glycidyl methacrylate copolymer with a Ti-bisphenolate type catalyst

Abstract

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.