A Study of Emulsion Polymerization Kinetics by the Method of Continuous Monomer Addition |
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Authors: | R A Wessling D S Gibbs |
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Institution: | 1. Physical Research Laboratory;2. Designed Products Research , The Dow Chemical Company , Midland , Michigan , 43640 |
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Abstract: | The differences in the kinetics of emulsion polymerization between nonswelling and swellable latex particles were explored in an attempt to define the locus of polymerization. The systems studied included vinylidene chloride, which forms a nonswelling particle, and mixtures of vinylidene chloride and butyl acrylate, which copolymerize to form a swellable particle. The basic experiment involved growing a seed latex by adding monomer at a constant rate. At low feed rates the rate of polymerization Rp was controlled by the rate of monomer addition Ra. The data fit the equation Rp?KRa where the proportionality constant had an average value of 0.91. K was not dependent on monomer composition and appears to be a constant characteristic of the monomer addition process. In the range where this relationship holds, the reaction runs starved, i.e., monomer is consumed almost as fast as it enters the reactor. At higher rates of addition the reaction floods and excess monomer in the form of droplets can be detected. In this condition the rate starts out at a lower value but increases with conversion.' Rp is not controlled by Ra but does depend on monomer composition. No major differences were found between the behavior of swelling and nonswelling systems. Neither followed che kinetics expected if the Smith-Ewart theory were applicable. The results argue strongly that polymerization takes place at the particle-water interface or in a surface layer on the polymer particle. |
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