Functional Nitroxyls for Use in Delayed-Onset Polyolefin Cross-Linking

Abstract

A new approach to controlling the dynamics and yields of polyolefin radical cross-linking is described, wherein 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (AOTEMPO) is used to quench macroradicals in the early stages of the process and to subsequently generate a covalent network through the oligomerization of polymer-bound acrylate functionality. Selectivity of alkyl radical trapping by AOTEMPO to give alkoxyamine intermediates in preference to acrylate addition products is discovered using model compound studies and through rheological measurements of linear low density polyethylene cross-linking. The latter demonstrate the ability of AOTEMPO to delay the onset of cross-linking while not compromising the cross-link density of the resulting thermoset. The influences of reagent loadings, peroxide decomposition rates, and the structure of polymerizable functionality are quantified and discussed.