Occlusion Heterogeneous Polymerization

In addition, Bamford, Jenkins and coworkers (19) previously reported on the behavior of occluded radicals in the heterogeneous polymerizations of acrylonitrile, methyl acrylate, methyl methacrylate and vinylidene chloride. From their electron spin resonance studies, they concluded that the degree of occlusion was ... 

Occlusion of growing radicals within the precipitated polymer has been emphasized by Bamford and co-workers (4) as the paramount factor in the kinetics of heterogeneous polymerization. The following argument endeavors to show that at least under the conditions discussed here the kinetic results can be accounted for by considering surface polymerization only. 

Bamford, Jenkins and co-workers [56] successfully interpreted the reactivity of trapped radicals by the occlusion theory for the heterogeneous polymerization of acrylonitrile. According to this theory, the probability of a radical becoming occluded by coalescence and the diffusion barrier within the precipitated polymer coils depends on their number and size, respectively. 

The bulk polymerization of acrylonitrile has been studied by numerous workers (for a literature survey on the problem see ref. j O and JL1J. The kinetic features of this reaction at room temperature are summarized in Table I. It is one of the typical examples of polymerization under heterogeneous conditions in which the anomalies are generally assumed to arise as a result of non-stationary conditions caused by the "occlusion" of growing chains in the precipitated polymer (10). The presence of occluded radicals was indeed demonstrated by 5R measurements (12) and by... 

Although the polymerization of AN in bulk and also in the presence of 5-15% alcohol was heterogeneous, that of MMA in the presence of the alcohol remained homogeneous. Radical occlusion undoubtedly took place in the AN polymerizations, but this complication has not been considered in detail. 

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