Cage effect (chemistry)

The cage effect in chemistry describes how the properties of a molecule are affected by its surroundings. First introduced by Franck and Rabinowitch in 1934, the cage effect suggests that instead of acting as an individual particle, molecules in solvent are more accurately described as an encapsulated particle. In order to interact with other molecules, the caged particle must diffuse from its solvent cage. The typical lifetime of a solvent cage is 10⁻¹¹s.

In free radical polymerization, radicals formed from the decomposition of an initiator molecule are surrounded by a cage consisting of solvent and/or monomer molecules. Within the cage, the free radicals undergo many collisions leading to their recombination or mutual deactivation. This can be described in the follow reaction:

${\displaystyle R-R^{k_{1}}\rightleftharpoons _{kc}R_{cage}\centerdot ,\centerdot R_{pair}\rightleftharpoons _{k_{Dfree}}^{k_{d}}2R\centerdot _{radicals}\rightarrow Products}$

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