The effect of stirring speed on the rate of the persulfate‐catalyzed polymerization of vinylidene chloride has been determined. It was found that the first‐stage rate decreases with increasing stirring speed, that the second‐stage rate increases with increasing stirring speed, and that the rate of the third stage is independent of stirring speed. These results, as well as those of an earlier paper, may be explained in the following manner. The second stage slow‐down results from monomer starvation, caused by slow diffusion from coalesced droplets. Recovery is caused by transfer of monomer at the time of collision between a polymer particle and a monomer droplet. These collisions are allowed when the repulsive forces between monomer droplet and polymer particle are reduced because of surfactant deficiency.

Physical changes which accompany the crystallization of isotactic polypropylenes have been observed by dilatometry and optical microscopy at temperatures between 120 and 160°C. Samples were fused at 220°C. and then held at a predetermined crystallization temperature for times ranging up to many hours. Rate constants for the crystallization were calculated from volume changes and from measurements of radial growth of spherulites. Polypropylenes from different sources exhibited quite different concentrations of spherulites and growth rates. Crystallization appears to proceed, at least at the higher temperatures, by spherical growth from a fixed number of nuclei, apparently arising from foreign matter in the polymer. With decreasing temperature, the number of nuclei (hence also the number of spherulites) increases, since apparently the conditions for nucleation become less critical. The crystallization follows the kinetics of a nucleation‐controlled process according to an Avrami equation, ‐log (1 ‐ ΔV / ΔV ∞) = kt3. Deviations from the third power of time at the lower temperatures may be the result of a secondary ordering process, slower than the primary crystallization.

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Certain pairs of surfactants interact in relatively concentrated aqueous solutions to give unexpectedly high viscosity. When nonsurfactant substances are added to such a surfactant pair, there may be either a further increase in viscosity or a decrease. Results of detergency tests of one surfactant pair in varying proportions are given.