Relative Reactivities of Elements of Polymer Chains, Determined by Their Transformation in Solution, Initiated by Dicumyl Peroxide

The kinetics of the degradation of polyisobutylene and polystyrene initiated by dicumyl peroxide in the undiluted state and in solvents of different composition has been studied. The degradation process was experimentally investigated by a viscosimetric method. The kinetic expression of the degradation carried out in such a way gives also the relative values of the rates of reaction of hydrogen atoms in polymers with radicals of the peroxide used, determined for polyisobutylene, polyethylene, polystyrene, and n‐heptane. The reactivities of CH 3 , CH 2 , and CH groups, calculated from the results, are in the ratio 1:6:17; the methine hydrogens of the polystyrene benzylidene groups are three times more reactive than hydrogens of the analogous ethylidene groups of polypropylene. The reactivity of the low molecular weight model substance, n‐heptane, is about 30% greater than would be expected from the sum of the reactivities of its elements determined from polymers. This fact suggests that the ability of macromolecules to enter into substitution reactions with free radicals is less than that of low molecular weight analogues.