The technique of pulsed-laser polymerization was used to measure the propagation rate coefficient (kp) of styrene in dimethyl formamide and acetonitrile over a range of monomer concentrations at 40 °C. A significant solvent effect was observed in both solvents. In dimethyl formamide, the kp value systematically falls, as the monomer concentration decreases, to a value that is (at 1 mol l-1 of styrene) approximately 75% of the bulk kp. In acetonitrile, the kp is also reduced. In this case, however, the kp value has a minimum at an intermediate dilution.
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We gratefully acknowledge the provision of density measurements for DMF by Dr. Robin Hutchinson, the measurement of the density of acetonitrile by Ms. Laura Eadie, support from the Australian Research Council, and the award (to M.L.C.) of an Australian Postgraduate Award.