A review of the kinetics of the low conversion, free‐radical termination process

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Abstract
A review of recent experimental and theoretical results exploring the free‐radical termination process in low conversion polymerization systems is presented. This very interesting and very specific, bimolecular termination step is vital in the development of free‐radical polymerization kinetics and is frequently assumed to operate independent of the reaction system. It is the authors' belief that a good deal of the scatter in low conversion kinetic parameter estimates prevalent in the current literature is due to the effect of nonideal free‐radical termination. While most current work is done in derivation of semi‐empirical correlations describing the magnitude of this effect, such methods lack generality since they, by design, ignore effects which are significant in describing the phenomena. Thus, the predictive ability of such models is compromised from the outset.A general discussion of accepted low conversion kinetic modelling structures and applicable theoretical development of the process by which free‐radical termination occurs at low polymer concentrations is included. A review of current activities in this field is then presented, with a description of experimental techniques, pertinent results, a list of dominant effects and conclusions. Finally, a simple and comprehensive model structure is introduced which will be useful in analyzing low conversion kinetics and predicting rates and molecular weights from a variety of effects.The intentions of this work are to order some of the more important results in the literature in the study of this particular reaction step and thus, provide some clarity and to demonstrate the sensitivity of this reaction step and its potential effect on kinetic predictions for free‐radical polymerizations.

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