Polymerization experiments with styrene in benzene at 60 ยฐ, initiated by benzoyl peroxide, covering a wide range of concentration of both monomer and initiator are reported; the results cannot be explained in terms of the classical rate relationship with Rp oc [I] tfz [MI. Deviations were reflected in unexpected orders of monomer up to [M] ~4 and of initiator down to [I] ยฐ42 when the initiator concentration is increased and monomer concentration is decreased. Based on the concept of primary radical termination, an equation, viz.
show a wide range of linearity; the characteristic constant kv, e/k~k v and alsofk can be obtained from the slope and intercept, respectively, kv,,, kl and kp are, respectively, the rate constants of primary radical termination, initiation and propagation and fk is the efficiency of initiation, defined as the fraction of radicals which come out of the solvent cage and take part in initiation, primary radical termination and primary radical recombination. The definition offk is thus differentiated from the conventional efficiency of initiation. Finally, we have derived an equation which allows determination of the classical efficiency of initiation as a function of [I]/[M] 2 and also allows a correction of R v in handling the above equation by taking into account the small amount of monomer consumed in initiation.