Inhibition mechanism and kinetics for an antioxidant type inhibitor, which can function only in the presence of oxygen, in the copolymerization of styrene and methyl methacrylate (MMA) are proposed. Experimental studies of the homopolymerizations with hydroquinone (HQ) and p‐tert‐butylpyrocatechol (TBC) as inhibitor at 50–70°C and of the copolymerization with HQ as inhibitor at 60°C show a good fit of the equations proposed and are self‐consistent, except for the homopolymerization system MMA/TBC, in which TBC can function also as an inhibitor even after the depletion of oxygen. The copolymerization system styrene (1)/MMA (2)/HQ shows a synergistic effect, positive for the rate of oxygen consumption and negative for the inhibition time. This can be attributed to the favored cross‐propagation of the peroxyl radicals, R1 O and R2 O , with the comonomers as indicated by the found reactivity ratios (both < 1; r1 = 0,275, r2 = 0,314). Detailed calculations using the proposed kinetic equations indicate that, if the cross‐propagation is not favored, the inhibition time will show a positive synergistic effect.
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Chen et al. (1986) studied this question.