Comparative Study of Particle Size in Suspension Polymerization and Corresponding Monomer−Water Dispersion

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Abstract

A comparative study of the suspension polymerization of methyl methacrylate and the corresponding nonreactive monomer−water dispersion was carried out. The main conclusion was that, even with a fully stabilized dispersion, the average sizes of drops/particles from the suspension polymerization and dispersion processes might not be the same. An increase in the viscosity of the drops during the early transition stage in a suspension polymerization is sufficient to enhance the drop stability against breakup and to increase the steady-state drop size in comparison with that in the nonreactive dispersion. Any change which leads to an increase in the rate of drop breakup, such as increasing the impeller speed and the stabilizer concentration, narrows the gap between the steady-state drop sizes in the reactive and nonreactive systems. It was shown that the information obtained from nonreactive monomer−water dispersion processes is quite useful in the analysis of events occurring in the course of corresponding suspension polymerizations. The degree of the stability of the drops in suspension polymerizations against coalescence or breakup was estimated by studying coalescence and breakup in corresponding monomer−water dispersion processes. The drop size exponent in terms of agitation speed changed from −1.24 for a fully stabilized dispersion to −0.74 for an unstable dispersion; these correspond to the breakup-dominant and coalescence-dominant regions, respectively. After polymerization, particle sizes from the stable suspensions were similar to the drop sizes found in the nonreacting dispersions, but particles from unstable suspensions were very large.

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