Nitroxide-mediated controlled radical polymerisation: towards control of molar mass Controlled Radical Polymerisation

The mechanism of the TEMPO-mediated controlled radical polymerization of styrene in bulk is discussed. It is shown that the isotropic correlation time (tc) of a nitroxide can be used as a measure of the diffusive rate coefficient of trapping (ketD). A general empirical relationship for the density of polystyrene as a function of molar mass and temperature is established to correct concentration data obtained from CRP experiments for volume contraction. It is demonstrated that the overall rates of polymerization of styrene in bulk do not show a dependence upon alkoxyamine concentration. Broadening of the molar mass distribution in a CRP experiment is ascribed to a low rate of alkoxyamine C-O bond homolysis and permanent chain-stopping reactions, e.g. bimolecular termination