The incorporation of aroyl peroxide fragments in polystyrene

Initiation of the solution polymerization of styrene by catalytic quantities of p‐chloro‐,p‐bromo‐, and p‐nitrobenzoyl peroxides leads to incorporation of catalyst fragments which are primarily (88–95%) aroyloxy groups. Use of p‐iodobenzoyl peroxide gives polymers of somewhat higher molecular weight and lower (79%) aroyloxy fragment content. This anomalous behavior of the iodo compound may be due to its rearrangement to an iodosobenzoate‐type compound. Treatment of polystyrene in benzene solution with these same peroxides leads to incorporation of catalyst fragments 96% chlorobenzoyloxy and 48% bromobenzoyloxy groups. p‐Nitrobenzoyl peroxide is not incorporated under these conditions. This is due to a scavenging action of the benzene solvent. p‐Iodobenzoyl peroxide again did not fit a general pattern and introduced 68% aroyloxy groups. In all of these reactions and increase in molecular weight of the polymer occurred. Treatment of bulk polystyrene with the peroxides led to incorporation of 70% chlorobenzoyloxy, 55% bromobenzoyloxy, and 3% p‐nitrobenzoyloxy groups. In these reactions the molecular weights of the polystyrene samples always decreased.