Radical chain polymerization overall scheme

Scheme of Radical Chain Polymerization 6.2.1 Overall Scheme... 

Radical chain polymerization, as noted above, is a chain reaction which involves mainly three steps - initiation, propagation, and termination, taking place in sequence. The overall scheme of the polymerization of a vinyl or related monomer M, initiated by the decomposition of a free-radical initiator I, may be schematically represented as follows (Ghosh, 1990) ... 

The synthesis of macromolecules by the free radical chain polymerization of low molar mass compounds, denoted as monomers, commences with the generation of free radicals, which is conveniently performed through photoreactions of initiator molecules. The subsequent processes, i.e. propagation, including chain transfer, and termination, are thermal (dark) reactions, which are not affected by light The simplified overall mechanism is described in Scheme 10.1. 

It can be seen from this scheme that in chain transfer, radicals are neither created nor destroyed. Consequently, the overall polymerization rate is unaffected by chain-transfer processes. However, as we shall see presently, it does limit the obtainable molecular weight. 

The general principle of the methods reported so far relies on a reversible activation-deacrivarion process between dormant chains (or capped chains) and active chains (or propagating radicals), with rate constants and fedeaci respectively (Scheme 5). Two main mechanisms of activation-deaaivation can be involved in C LRP, sometimes concomitantly reversible termination (i.e, dissociation-combination cycles) and reversible transfer. Hie overall reaction of DT polymerization with alkyl iodide (R-I) is depicted in Scheme 6. Written in this form, it is formally equivalent to telometiza-rion. However, the mechanism of DT polymerization... 

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