The role of excess nitroxide in the SG1 (N-tert-butyl-N-[1- diethylphosphono-(2,2-dimethylpropyl)] nitroxide)-mediated polymerization of methyl methacrylate

Methyl methacrylate (MMA) polymerizations have been conducted in the presence of large excesses of N-tert-butyl-N-[1-diethylphosphono-(2,2- dirnethylpropyl) nitroxide] (SG1) at 110°C. It is demonstrated that such a protocol does not improve control/livingness in the nitroxide mediated polymerization (NMP) of this monomer, instead substantial levels of disproportionation between the nitroxide and propagating radical (PMMA·) results. The extent of the disproportionation reaction increased with the SG1 concentration, eventually becoming the sole end forming event. Significant disproportionation between SG1 and PMMA· was also observed at substantially lower temperatures (45°C) in the presence of large excesses of SG1.