22. Polymerization in Microemulsions

Polymerization in microemulsions allows the synthesis of ultrafine latex particles in the size range of 5 to 50 nm with a narrow size distribution [33], The deposition of an ordered monolayer of such spheres is known to be increasingly difficult as the diameter of such particles decreases [34], Vigorous Brownian motion and capillary effects create a state of disorder in the system that is difficult... 

Polymerization in microemulsion has developed into a powerful technique for the preparation of strictly spherical micronetworks [1,2]. The final size of the polymerized particles is solely governed by the ratio of surfactant to monomer concentration, i.e., the fleet ratio S. To predict the final particle size at full conversion, two simple models for the polymerization in microemulsion have been proposed which differ only in some minor details. One of the models considers variable headgroup contributions to the particle radius [3]. This calculation finally arrives at Eq. 1. 

Polymerization in microemulsion systems has recently gained some attention as a consequence of the numerous studies on microemulsions developed after the 1974 energy crisis (1,2). This new type of polymerization can be considered an extension of the well-known emulsion polymerization process (3). Hicroemulsions are thermodynamically stable and transparent colloidal dispersions, which have the capacity to solubilize large amounts of oil and water. Depending on the different components concentration, microemulsions can adopt various labile structural organizations -globular (w/o or o/w tyne), bicontinuous or even lamellar -Polymerization of monomers has been achieved in these different media (4-18),... 

Styrene polymerization in microemulsions yields a different morphology compared to bulk polymerization. Preliminary results have been reported earlier (24.251. The solids obtained by polymerization of microemulsions are opaque, as opposed to transparent polystyrene obtained from bulk polymerization. The opacity is due to the presence of the surfactant. SEM micrographs imUcate porous structures in the solid materials obtained by jwlymeriang microemulsions. Figure 5(a) shows the structure of styrene polymeriz in bulk. As expected, it... 

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

Co, C.C., de Vries, R. and Kaler, E.W. (2001) Free-radical polymerizations in microemulsions. In J. Texter (ed), Reactions and Synthesis in Surfactant Systems. Marcel Dekker, New York, pp. 455-470. 

Candau E. Polymerization in microemulsions. In Kumar P, Mittal KL, editors. Handbook of Microemulsion Science and Technology. New York Marcel Dekker luc 1999. p 679. 

In this paper I review the salient features of polymerization in microemulsions at the present state of knowledge. I discuss the formulation of polymerizable microemulsions and show how the incorporation of monomers can modify the initial structure of the systems. The kinetic and mechanistic aspects are given and compared to those experienced in conventional emulsion polymerization. I also describe some recent results obtained on the formation of porous solid materials and functionalized microlatex particles, which seem quite promising for future applications. 

Gan and Chew [37,38] extended their studies to microemulsions in which all the components except water were polymerizable. Polymerization in microemulsions containing a polymerizable surfactant (sodium acrylamidoundecanoate [37] or acrylamidostearate [38]), a cosurfactant (acrylic acid), and methyl methacrylate as the continuous phase led, under certain conditions, to transparent solid terpolymers with up to 10-20% water dispersed in the polymer matrices. As in the case of copolymers, no particular structure was shown by SEM for these terpolymers. 

Polymerization in microemulsions with a water/oil droplet structure yields closed-cell porous polymeric solids having a morphology characterized by a disjointed cellular structure in which the water pores are distributed as discrete pockets throughout the solid. 

Polymerization in microemulsions with a bicontinuous structure results in a polymers with an open-cell structure, i.e., an interconnected porous structure with water channels through the polymer. The surface area increases steadily as water content increases in the precursor microemulsion. 

Candau, E, Polymerization in microemulsions, in Polymerization in Organized Media, C.M. Paleos (ed.), Gordon and Breach, Philadelphia, 1992, p. 215 ff. 

With respect to the polymerization in microemulsion there is the question about the actual monomer concentration which seems to be smaller than the nominal For a comparison of the kp values obtained from homogeneous and hetero-... 

Candau, F., Polymerization in microemulsions, in Handbook of Microemulsion Science and Technology, Kumar, P., Mittal, K. L. (Eds), Marcel Dekker, New York, 1999. 

Antonietti, M., Basten, R. and Lohnmann, S., Polymerization in microemulsions - a new approach to ultrafine, highly functionalized polymer dispersions, Macromol. Chem. Phys., 196, 441 (1995). 

Despite a big lack of imderstanding polymerization in microemulsion leads to model micronetworks which are easily surface-functionalized to radical macroinitiators or to ionic microgels. The macroinitiators have been utilized to obtain core-shell or star-like structures. 

M. Antonietti, W. Bremser, D. Mueschenbom, C. Rosenauer, B. Schupp, and M. Schmidt, Synthesis and size control of polystyrene latices via polymerization in microemulsion. Macromolecules 24, 6636-6643... 

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