Controlled Radical Grafting: Nitroxyl-Mediated Maleation of Model Hydrocarbons

Abstract

An exploration of nitroxyl-mediated polymerization principles for the synthesis of maleated polyethylene (PE) and polybutadiene (PBD) is presented. Thermolysis and disproportionation rates for eight alkoxyamines of relevance to PE and PBD modification are reported, including heptan-3-yl- and hept-5-en-3-yl-based alkoxyamines of 2,2,6,6-tetramethylpiperidinyloxyl, 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl, and 1,1,3,3-tetramethylisoindolin-2-yloxyl. The mediation of heptan-3-yl radical activity was complicated by extensive disproportionation of the alkoxyamines to olefin and the corresponding hydroxylamine. The hept-5-en-3-yl-based alkoxyamines underwent C−O bond homolysis without incurring significant disproportionation, and the addition of maleic anhydride (MAn) to the liberated allylic radical proceeded at a rate comparable to that of nitroxyl trapping. However, rapid disproportionation of the succinyl-based alkoxyamines arrested grafting after a single MAn addition. The consequences for controlled radical grafting of maleic anhydride to polymers are discussed.