Emulsion polymerization heat transfer aspects

The reaction engineering aspects of these polymerizations are similar. Excellent heat transfer makes them suitable for vinyl addition polymerizations. Free radical catalysis is mostly used, but cationic catalysis is used for non-aqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads, is directly suitable for some applications (e.g., paints, gel-permeation chromatography beads, expanded polystyrene). Most of these polymerizations are run in the batch mode, but continuous emulsion polymerization is common. 

It was stated at the beginning of this topic that heat management and safety aspects are important for the selection of the most suitable polymerization process. As the effectiveness of heat transfer is largely governed by the viscosity of the reaction mixture it is instructive to compare typical viscosities versus monomer conversion plots for the various polymerization processes that have been described above (Figure 5.3.13). Obviously, the most critical process with respect to heat removal is polymerization in-substance, while suspension and emulsion polymerizations show only very small changes in viscosity and thereby allow proper heat transfer even at high monomer conversions. 

In addition to batch emulsion polymerization (which is commonly used in the laboratory to study reaction mechanisms) for preliminary development/screen-ing of new latex products and to obtain approximate kinetic data for process development and reactor scale-up, the versatile semibatch and continuous emulsion polymerization processes are widely used for the production of commercial latex products. A major reason that batch reactors are not used for commercial production is due to the very exothermic nature of free radical polymerization and rather limited heat transfer capacity in large-scale reactors. Furthermore, continuous and especially semibatch reaction systems offer the operational flexibility to produce latex products with controlled polymer composition, particle morphology, and particle size distributions. These parameters will have an important influence on the performance properties of latex products. In this chapter, we will focus on the aspects of polymerization mechanisms and kinetics involved in semibatch and continuous emulsion polymerization systems. Those who are interested in the previous studies of semibatch and continuous emulsion polymerization processes should refer to the review articles cited in references 1. ... 

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