Kinetic characteristics of methylene quinones as inhibitors of polypropylene oxidation

Abstract The inhibiting activity of seven 2,6-di-tert-butyl-4-methylene quinones substituted in the α-position has been investigated in the course of the iniated oxidation of isotactic polypropylene at 115°. All the methylene quinones, apart from the one with the two phenyl substituents in the α-position, inhibit oxidation by chain termination reactions either with peroxide radicals alone, or with peroxide and alkyl radicals. Depending on the methylene quinone structure and on the partial oxygen pressure the stoichiometric inhibition coefficient varies from 1 to 6. The ratio of the rate constants for termination and propagation reactions falls in the range 10 4 –10 3 , which is close to the values for phenols of similar structure. Methylene quinone with the CH 3 group in the α-position is rapidly transformed to phenol.