Abstract
The dependence of exchange rate constants and diffusion coefficients of stable macroradicals (modified polydimethylsiloxane ( P = 15, 29, 97 ) and polyethylenoxide ( P = 25, 47, 140 ) on the length of polymer chain in various solvents is investigated. The results are compared with the rate constants for diffusive bimolecular recombination of macroradicals of various lengths. The dependence of rate constants of exchange and combination for macroradicals of different lengths obey the same law. The rate of combination for macroradical with P = 15-10 5 is shown to depend mainly on the mobility of an active centre, limited by diffusion of the whole macromolecule. The diffusion rate constant of combination can be described by the Smoluchowski equation in which the radius of an active centre is used as the effective radius of interaction. A model of bimolecular termination of macroradicals, a model of “freely penetrating coils” (FPC), is proposed. It implies that k ter ∼ P −0.9 ± 0.1 (for “good” solvents). The reactivity of an active centre in recombination is independent of the length of a macroradical chain for P > 15. The exchange interaction in a radical pair broadens the ESR lines of radicals and recombination with equal effectiveness.
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