Abstract
Photoinduced elementary reactions of low-MW compounds in polymers is an area of active research. Cured organic polymer coatings often undergo photodegradation by free-radical paths. Besides practical importance, such studies teach how the polymer environment controls elementary free-radical reactions. Presented here is a review of recent literature which reports such studies by product analysis and by a time-resolve technique of photochemical reaction inside the cage of a polymer and in the bulk of a polymer. It was established that application of moderate external magnetic field allows the control of the kinetics of free radicals in elastomers. Preheating and stretching of elastomers affect reactivity of photoproduced radicals.
Highlights
A description of cage effect usually starts with the first publication on this subject
The notion of cage effect is widely used in the kinetics of elementary liquid phase and especially free-radical reactions
The radicals not reacted in a cage exit into the polymer bulk and participate in random recombination in free-radical pairs (F-pairs)
Summary
A description of cage effect usually starts with the first publication on this subject. Molecules/radicals A and B are generated at distance close to or somewhat larger than a sum of their van der Waals radii ρA + ρB The latter sum is considered as a reaction radius ρ12. The notion of cage effect is widely used in the kinetics of elementary liquid phase and especially free-radical reactions. Cage effect value φ is a fraction of photogenerated molecules (radicals) recombined within a cage to the total number of generated radicals. A caged pair of radicals is formed in the same spin state as its excited precursor, that is, in a singlet or in a triplet state. Singlet (S)–triplet (T) interconversion of RPs (Equation (3)) during τc adds spin chemistry and magnetochemistry to the kinetics of elementary radical reactions in the condensed phase. There are a number of review articles dedicated to the cage effect [2,3,4,5,6,7,8]
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