Abstract
Many of today's industrial applications of emulsion polymers require the creation of polymer particles with specifically designed structures. A fair amount of work has been done on predicting and controlling particle morphology, and it is recognized that the reaction kinetics often play an important role in determining that morphology. The present work describes a procedure to calculate the reaction rate for two‐phase latex particles by extending the classic Smith–Ewart concepts to the more complicated situation. The model involves a complete account of radical events in both polymeric phases. Eight rate parameters are necessary to completely describe the system. A particle population distribution is generated to reflect the probability of specific particles to have two distinct numbers of radicals in each phase. Simple statistics on this population allow the calculation of the average number of radicals for each polymeric phase. The model collapses to the correct answers when applied to single‐phase particles and results in the prediction of the number of radicals in each of the phases when applied to structured particles. Several examples are described for core–shell (or inverted core–shell) and hemispherical particles in which the polymer Tg, monomer concentration and radical entry rates are varied. In addition, the effects of radical transfer rates between the polymer phases are highlighted. Such effects are found to be important for some polymer systems and not so important for others. The model is readily extendible to occluded structures. Since the reaction kinetics are concluded to be significantly dependent upon the particle morphology, it is clear that morphology development and reaction kinetics are coupled processes and need to be treated simultaneously in order to produce an effective overall model for two‐phase emulsion polymers.
Acknowledgments
We are grateful for the financial support of the University of New Hampshire and for the helpful discussions with Professor A. N. Venkatachalam and Professor Claire Durant.