No abstract

A theoretical relation has been derived for the equilibrium swelling of latex particles. The equilibrium solubility and rate of solution of solvents were measured on a series of polystyrene latex fractions of varying particle size. The solvents used were styrene, toluene, and chlorocyclohexane. It was found, as predicted by theory, that the equilibrium amount of solvent imbibed by latex particles is a direct function of the particle diameter and an inverse function of the interfacial energy at the surface of the particles. The molecular weight of the polymer has no effect on the equilibrium swelling, within the range from 100,000 to several million molecular weight units. The rate of imbibition of these solvents appears to be extremely rapid, indicating that equilibrium solubility would appear to be maintained in most polymerization reactions. The fact that a particular solvent is a “good” solvent for the polymer does not necessarily result in a greater swelling of the particles, since the solvent may show a higher interfacial energy against the aqueous phase. The soap titration method is best for determining the average particle size of a latex for purposes of predicting equilibrium swelling.

The mechanism of emulsion polymerization of chloroprene has been found to differ considerably from that of other monomers such as styrene or butadiene, apparently due to its exceptional reactivity. Whereas the formation of polymer particles from monomers of low water solubility usually depends largely on the solubilizing effect of detergent micelles, this is not the case for chloroprene. It has been found that dissolved chloroprene and the chloroprene‐water interface may both be active loci for the initiation of polymer particles, depending upon the conditions of the polymerization reaction. It has also been found that chloroprene does not obey the “ideal” kinetics as proposed by the Smith‐Ewart theory, since the rate of particle is not independent of the type and amount of initiator present. Possible reasons for this deviation are suggested.