Nitroxide-mediated polymerization of methyl methacrylate and styrene with new alkoxyamines from 4-nitrophenyl 2-methylpropionat-2-yl radicals

The N-phenylalkoxyamine N-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethoxy)-N- (1-methyl-(1-(4-nitrophenoxy)carbonyl)ethyl)benzenamine (1) was prepared by the addition of 4-nitrophenyl 2-methylpropionat-2-yl radicals across the double bond of nitrosobenzene and evaluated as an initiator for nitroxide-mediated polymerization (NMP). N-Phenylalkoxyamines have not been extensively studied in NMP, though they have shown promise in controlling methyl methacrylate (MMA) polymerization to moderate conversions. It is thought that delocalization of the nitroxide radical through the N-phenyl substituent may minimize cross-disproportionation of the nitroxide with the chain end that has made NMP of MMA difficult. Here, we show that alkoxyamine 1 is capable of controlling the NMP of MMA to 50% conversion while maintaining narrow molecular weight distributions (M_w/M_n = 1.12-1.30). Additionally, chain extension from the resulting PMMA macroinitiators with MMA or styrene allows the formation of diblock copolymers. The corresponding N-tert-butylalkoxyamine, 2,2-dimethyl-3-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethoxy)-4-methyl-(4-(4- nitrophenoxy)carbonyl)ethyl-3-azapentane (2), was synthesized by the addition of 4-nitrophenyl 2-methylpropionat-2-yl radicals across the double bond of 2-methyl-2-nitrosopropane. Polymerization of MMA with alkoxyamine 2 was uncontrolled, which suggests the paramount importance of the N-phenyl group for MMA polymerizations.