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synopsisThe quantitative theory of the f-radical mechanism in emulsion polymerization is reexamined. A mechanism involving desorption and reabsorption of radicals is discuased.The average number of radicals per particle has been calculated as a function of three parameters. A simplified, approximate solution for the average number of radicals per particle is given for cases where this number is low.

An investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed. The effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C. The order of reaction with respect to initiator was found to be 0.5. The rate of reaction was found to increase with increasing conversion. The number of latex particles was found to be constant during the polymerization, between 10 and 90% conversion, and also found to be independent of the concentration of initiator. The order of reaction with respect to the number of particles was found to increase from 0.05 to 0.15 in the range investigated (Nw = 1016‐1019 per liter H2O). The order decreases slightly with increasing conversion. A mechanism involving a rapid desorption and reabsorption of radicals in the latex particles is proposed. A marked increase in rate was observed at about 70–80% conversion. A closer investigation of this phenomenon was performed by a continuous addition of vinyl chloride at a pressure below the saturation pressure of vinyl chloride corresponding to the reaction temperature. It appeared that under such conditions reaction rates of about twice those of the ordinary runs might be obtained. No change in the number of particles was observed, either during the polymerization or compared to the ordinary run at the same concentrations of emulsifier and initiator. The effect of the degree of reduction in the pressure of vinyl chloride was also investigated. It was found that the rate of reaction passed through a maximum at a pressure of about 6.75 atm, as compared to 7.75 atm in an ordinary run (Saturation pressure of vinyl chloride at 50°C).

The swelling capacity of aqueous dispersions of particles (or droplets) containing a relatively low molecular weight, highly water‐insoluble compound (Y) may be more than a thousand times higher than that of particles consisting of polymer only. The rate, and also the degree of swelling, may furthermore be increased by having the swelling substance, which usually is a low molecular weight, slightly water soluble substance, present in a finely dispersed form. A two‐step swelling process has been described. In a first step, relatively small monodisperse polymer particles are swollen with a component Y and then with monomer or monomer mixtures, followed by polymerization. The method allows preparation of highly monodisperse particles of more than 50 μm diameter with a standard deviation of less than 2%. The particles may be prepared as core and shell particles of different density and with various surface layers, or as macroporous particles. The new particles have found application as standards in immunoassays and, most important up to now, in liquid chromatography. An extension of the process allows the production of monodisperse magnetizable particles which have found application in cell separation of cancer cells from normal cells.