New chemistry for preparing polypropylene (PP) thermosets is described, wherein radical degradation suffered during conventional peroxide treatment is overcome using a nitroxyl additive that bears a polymerizable functional group. A small amount of 4-vinylbenzoic-2,2,6,6-tetramethylpiperidin-N-oxyl (VBTEMPO) is used to trap peroxide-derived, alkyl radical intermediates during the early stages of the modification process, yielding a macromonomer derivative that crosslinks in the post-quenching phase through side-chain oligomerization. This process produces thermosets of a PP homopolymer with gel contents in excess of 90%, while providing the induction period needed to shape the formulation before the melt viscosity increases. Furthermore, a preliminary accelerated oxidation study suggests that the polymer-bound N-alkoxyamine functionality generated by this process can confer oxidative stability to the thermoset product. (C) 2017 Elsevier Ltd. All rights reserved.