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Various models have been proposed in order to understand different physical and chemical events taking place during emulsion copolymerization. One of the important processes involved is the entry of radicals into particles, which is often described using the model of Maxwell and Morrison. For emulsion homopolymerization, experimental data partly support this model, while for emulsion copolymerization not many experimental data are available. Here, the different models that have been established over the past decades are reviewed with an emphasis on the propagational mechanisms involved during the entry of oligomeric radicals into latex particles in emulsion homopolymerization. An answer is given to the title question: “Can the existing models be verified?”. magnified image

For the first time a new analytical procedure to analyze small oligomers produced in a butyl acrylate‐methyl methacrylate emulsion copolymerization is applied. With this method, low molecular weight co‐oligomers are studied using MALDI‐ToF‐MS. Both the oligomers in the aqueous phase and the oligomers in the particle phase can be seen. Varying the initiator system, it is observed that the initiation step has an influence on the composition of these oligomers and hence on the absorption on to latex particles. Chain length dependent average compositions in the aqueous phase are observed. The chain length dependent oligomer composition can be described in terms of kinetic effects and preferential/selective adsorption of co‐oligomers on the particle surface. The kinetic effects and the extent of adsorption on the particle phase are both dependent on the various end groups. The preferential/selective adsorption of co‐oligomers on the particle phase is explained on the basis of solubility and interactions with the surface. The chain length dependent absolute oligomer amount decreases exponentially with chain length as confirmed by Monte Carlo simulations. This information is important to further understand the events of the aqueous phase of an emulsion copolymerization as well as the entry of radicals into the particles.

In emulsion copolymerizations, the two monomers might not be equally incorporated in the copolymers. Besides copolymerization in the particles, also copolymerization in the aqueous phase can take place which affects the formation of oligomeric radicals responsible for the entry of radicals into the particles. In describing copolymerization in emulsion polymerization, one can use the normal reactivity ratios in combination with the monomer feed ratios in the phase at hand (either water phase or particle phase). Most of the research works done were focused on the feed ratio of the monomers in the particle phase. is is because of the interest in the �nal product. But in case of water-soluble monomers, where signi�cant amount of polymerization already occurs in the water phase, feed ratios of monomers in the water phase have to be known. Even for less water-soluble monomers, the feed ratios in the aqueous phase are important to know, related to entry of radicals. erefore, to calculate feed ratios in water phase, solubilities of mixtures of monomers in this phase have been measured by using a UV-Vis technique. It is shown that the solubility of one monomer is in�uenced by the presence of another monomer.

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