Nitroxide-mediated radical polymerization of styrene: experimental evidence of chain transfer to monomer

Chain transfer to monomer during nitroxide-mediated radical polymerization of styrene has been investigated for 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) mediated polymerizations at 125 and 110 °C, respectively. A novel technique employing a fluorescence-labelled polystyrene-TEMPO macroinitiator enabled separate detection of the total chain distribution and the distribution of chains containing the original macroinitiator, thus directly confirming the presence of chains not containing macroinitiator. Chain transfer to monomer results in a low molecular weight tail, which can be very much pronounced, in particular in the number distributions. Quantitative analysis of the total number of chains in both the TEMPO and the SG1 systems, correcting for the contribution of thermal initiation of styrene, yielded chain transfer to monomer constants in agreement with the literature.