Reactivity of condensed‐ring hydrocarbons as polymerization retarders

Abstract

AbstractSeventeen condensed‐ring hydrocarbons have been investigated as retarders or inhibitors of styrene and methyl methacrylate polymerization. Rates were measured dilatometrically. Nine of the compounds tested retarded or inhibited the polymerization of styrene, but methyl methacrylate appears not to be affected by this class of substances. Styrene data obtained are examined in the light of Fukui's “frontier electron” formalism for correlating structure and reactivity. It is concluded that the principal locus of radical attack is at the meso carbon atoms, Fukui's (Ss) region, and that a substantial value of the (Ss) density index is required for retardation, although when the molecule also possesses an appreciable (Sp) index, a synergistic action is noted. The point is made that since condensed‐ring hydrocarbons do not have “functional groups” in the sense that quinones and other retarders do, the effect of monomer reactivity is likely to be of added importance in determining retarder efficiency. The lack of retardation effects in polymerizing methyl methacrylate is interpreted from this standpoint. A reverse chaintransfer reaction is tentatively proposed to account for the observed behavior.