The polymerization of methyl methacrylate initiated with AIBN and inhibited with cupric bromide in DMF has been studied at from 40–70°C. Rate constants for the initiation reaction, obtained by the inhibition period method, were 6.2 × 10–7, 3.7 × 10–6, 1.42 × 10–5 and 8 × 10–5 s–1 at 40, 50, 60 and 70°C respectively, yielding an activation energy of 137.5 kJ mol–1. The acceleration period following complete inhibition was rapid and became distributed due to self-heating effects when ordinary dilatometers were used. Disc-bulb dilatometers helped to removed this distortion. Values of the ratio where kx/kp, where kx is the rate constant from the reaction between polymethyl-methacrylate radicals and the cupric salts, were greater than those obtained using cupric chloride as an inhibitor.