Emulsion polymerization principal possibility

The theory also has relevance to the so-called seeded " emulsion polymerization reactioas- In these reactions, polymerization is initial in the presence of a seed latex under conditions such that new particles are unlikely to form. The loci for the compartmentalized free-radical polymerization that occurs are therefore provided principally by the particles of the initial seed latex. Such reactions are of interest for the preparation of latices whose particles have, for instance, a core-shell" structure. They are also of great interest for investigating the fondamentals of compartmentalized free-radical polymerization processes. In this latter connection it is important to note that, in principle, measurements of conversion as a function of time during nonsteady-state polymerizations in seeded systems offer the possibility of access to certain fundamental properties of reaction systems not otherwise available. As in the case of free-radical polymerization reactions that occur in homogeneous media, investigation of the reaction during the nonsteady state can provide information of a fundamental nature not available through measurements made on the same reaction system in the steady state. 

An emulsion has been defined above as a thermodynamically unstable heterogeneous system of two immiscible liquids where one is dispersed in the other. There are two principal possibilities for preparing emulsions the destruction of a larger volume into smaller sub-units (comminution method) or the construction of emulsion droplets from smaller units (condensation method). Both methods are of technical importance for the preparation of emulsions for polymerization processes and will be discussed in more detail below. To impart a certain degree of kinetic stability to emulsions, different additives are employed which have to fulfil special demands in the particular applications. The most important class of such additives, which are also called emulsifying agents, are surface-active and hence influence the interfacial properties. In particular, they have to counteract the rapid coalescence of the droplets caused by the van der Waals attraction forces. In the polymerization sense, these additives can be roughly subdivided into surfactants for emulsion polymerization, polymers for suspension and dispersion polymerization, finely dispersed insoluble particles (also for suspension polymerization), and combinations thereof (cf. below). 

To fix an emulsion by polymerization requires precautions in two aspects (i) to enhance emulsion stability, and (ii) to choose a rapid polymerization process advancing from the interface into the droplet core. Thus, the fixation of droplets by polymerization is in principal possible. The crucial parameters are droplet size and size distribution, viscosity of both phases, and the polymerization procedure. It is perfectly possible to fix a droplet size distribution in the pm-sizerange, typical for... 

Surfactants (emulsifiers of various chemical nature) are usually applied as stabilizers of disperse systems, they are rather stable, poorly destmcted under the influence of natural factors, and contaminate the environment. The principal possibility to synthesize emulsifier-free latexes was shown. In the absence of emulsifier (but in emulsion polymerization conditions) with the usage of persrrlfate-lype irritia-tors (e g., ammonirrm persulfate), the particles of acrylate latexes can be stabilized with ionized endgroups of macromolecules. The ion radicals appearing in... 

Notwithstanding that it is usual to carry out the emulsion polymerization under acid conditions, and that this requirement is usually assumed to rule out the possibility of using carboxylate soaps as surfactant, a process has been developed for effecting the emulsion copolymerization at pH values of 7 or below using carboxylate soaps as the principal surfactant (25). 

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