Polyethylene Crosslinking Using the Epoxy‐anhydride Reaction I: A Strategy for a Curing Process with High Thermal Sensitivity

The initiated epoxy-anhydride reaction was examined as a crosslink motif for effecting cure in functionalized polyethylene for electrical cable insulation applications. A specific challenge for this application is that little to no crosslinking can occur during the processing steps (similar to 140 degrees C), but crosslinking must be rapid and complete within a few minutes during the curing process (similar to 200 degrees C). To achieve this, we coupled the kinetics of the formation of an initiator for the epoxy-anhydride reaction to the crosslinking step to achieve a phenomenological temperature sensitivity or "latency" that would be difficult to access via a single simple reaction. Evaluations of different imidazolium and phosphonium salts as initiator precursors were conducted with model compounds in solution, and specific salts were chosen for polymer studies based on the ratio of the phenomenological rates measured for the model reaction at similar to 440 degrees C and similar to 200 degrees C. In polymer studies using epoxide-functional poly(ethylene), high crosslinking rates were observed at similar to 200 degrees C while crosslinking was minimal at similar to 140 degrees C. However, inclusion of the anhydridefunctional polyethylene in the formulation led to loss of initiator latency, and significant crosslinking was observed at similar to 140 degrees C. A reaction between the anhydride or an impurity and initiator precursor is postulated to produce a kinetically-competent initiator at lower temperatures that destroys latency.