Popcorn polymer, growth

This paper reviews some of the more basic contributions over the past 20 years or so to the study of popcorn polymers. Some results from the authors9 laboratories are then presented in an attempt to characterize further the nature of these polymers and their growth mechanisms. These more recent results include those obtained by studies of the popcorn polymers using the polarizing and electron-scanning microscopes and ESR measurements. The importance of crosslinking and entanglements is discussed, and industrial applications—present and potential— are considered. 

The occurrence of straining in a microscopic range was shown by Breitenbach, Preisinger, and Tomschik (9), and further microscopic studies of popcorn polymer formation and growth were carried out by Breitenbach and coworkers (10). 

At later growth stages, strains are also induced in the surrounding polymer gel. Figure 6 may show the first step in the transformation of a preformed glassy polymer into a popcorn polymer. 

Under the most favorable conditions, the formation of a popcorn polymer particle is a highly improbable process for 1016 molecules of polymer produced in the system, only one popcorn polymer particle has been grown, possibly from a single macromolecular precursor. By contrast, growth under optimum conditions is a fast process and approximately obeys the relation—given by Welch et al. (4)—for butadiene popcorn polymer ... 

One reaction of popcorn polymers is their very rapid, proliferous growth in appropriate monomers. The rapid growth reaction corresponds to a relatively high content of the growing material on radical chain ends. It is possible to measure the growth rate directly by ob-... 

It is possible to obtain popcorn polymers in the form of flakes (24). For this purpose, a pulverized popcorn polymer is brought into the monomer feed in a stirred reactor. The proliferous growth of the seed material in the stirred reactor leads to a finely distributed material... 

The thermal decay process of the radicals is a bimolecular reaction. The decay rate increases with increasing temperature. At 100° C, a half-life of 12 minutes has been observed for methyl methacrylate popcorn radicals. A fast decay rate takes place when the dry popcorn is swollen in a liquid such as benzene. That means that during the proliferous growth process, when the polymer is swollen by the monomer, a decay process also occurs, and a stationary radical concentration in the growing polymer popcorn results. A liquid that does not swell the polymer (for example, methanol for polystyrene) does not influence the decay rate. A much higher rate of radical decay is obtained with a benzene solution of diphenylpicrylhydrazil. The reaction rate between the polymer radical and inhibitor radical may be measured. 

Chu F, Yamaoka T (1996) Polychloroprene popcorn growth kinetics measured by the McBain balance. Polymer 37 537-539... 

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