Kinetics of polymerization of styrene initiated by substituted peroxides. II. Decomposition rate constants and efficiencies

The following bis‐substituted benzoyl peroxides were used as initiators for the polymerization of bulk styrene monomer at 90°C.: p‐methoxy‐, p‐methyl‐, p‐chloro‐, m‐bromo‐, 3,4‐dichloro‐, p‐cyano‐, and p‐nitro‐; in addition, unsubstituted benzoyl peroxide was also studied. From the observed rates of polymerization the rate constants for the unimolecular decomposition and for the radical‐induced decomposition of the peroxides were obtained, as well as the efficiency of initiation of polymerization. It was observed that substituents more electron‐withdrawing than p‐chloro did not change the unimolecular rate constant. Conversely, substituents less electron‐releasing than p‐chloro had little effect on the efficiency of initiation. The induced decomposition rate constant gave a simple linear Hammett plot with positive slope.