Recombination Kinetics of Radicals in Polymers: Magnetic Field Effects

Abstract

The results of kinetic studies of the recombination of radicals in the cage and in bulk of polymers obtained by nanosecond laser photolysis are summarized. The films of rubbers (poly(ethylene-co-butylene)), biaxially oriented polypropylene depending on the preliminary heat treatment, polystyrene, craton (polystyrene-block-poly(ethylene-butylene)-block-polystyrene), silicones, and acrylates are studied. By direct observation, the significant effect of the magnetic field on the kinetics of the recombination of radicals both in the cage and in the bulk of rubber films is recorded. Stretching the rubber film significantly delays the escape of radicals from the matrix cage and, accordingly, bimolecular recombination in the bulk (when stretched 3 times, both processes slow down by a factor of 2). The effect is significantly higher that that expected based on the change in the free volume of the polymer. The increased content of polypropylene in the rubber leads to a stronger cage effect due to the slower escape of radicals into the bulk; at the same time, the recombination rate in the bulk increases and the reaction takes place in the restricted areas of the polymer matrix. The comparative analysis of the kinetic characteristics in polymer of different classes is carried out.