Polymer latex particles are nanofunctional materials with widespread applications including electronics, pharmaceuticals, photonics, cosmetics, and coatings. These materials are typically prepared using waterborne heterogeneous systems such as emulsion, miniemulsion, and suspension polymerization. However, all of these processes are limited to water-stable catalysts and monomers mainly polymerizable via radical polymerization. In this Account, we describe a method to overcome this limitation: nonaqueous emulsions can serve as a versatile tool for the synthesis of new types of polymer nanoparticles. To form these emulsions, we first needed to find two nonmiscible nonpolar/polar aprotic organic solvents. We used solvent mixtures of either DMF or acetonitrile in alkanes and carefully designed amphiphilic block and statistical copolymers, such as polyisoprene- b-poly(methyl methacrylate) (PI- b-PMMA), as additives to stabilize these emulsions. Unlike aqueous emulsions, these new emulsion systems allowed the use of water-sensitive monomers and catalysts. Although polyaddition and polycondensation reactions usually lead to a large number of side products and only to oligomers in the aqueous phase, these new conditions resulted in high-molecular-weight, defect-free polymers. Furthermore, conducting nanoparticles were produced by the iron(III)-induced synthesis of poly(ethylenedioxythiophene) (PEDOT) in an emulsion of acetonitrile in cyclohexane. Because metallocenes are sensitive to nitrile and carbonyl groups, the acetonitrile and DMF emulsions were not suitable for carrying out metallocene-catalyzed olefin polymerization. Instead, we developed a second system, which consists of alkanes dispersed in perfluoroalkanes. In this case, we designed a new amphipolar polymeric emulsifier with fluorous and aliphatic side chains to stabilize the emulsions. Such heterogeneous mixtures facilitated the catalytic polymerization of ethylene or propylene to give spherical nanoparticles of high molecular weight polyolefins. These nonaqueous systems also allow for the combination of different polymerization techniques to obtain complex architectures such as core-shell structures. Previously, such structures primarily used vinylic monomers, which greatly limited the number of polymer combinations. We have demonstrated how nonaqueous emulsions allow the use of a broad variety of hydrolyzable monomers and sensitive catalysts to yield polyester, polyurethane, polyamide, conducting polymers, and polyolefin latex particles in one step under ambient reaction conditions. This nonpolar emulsion strategy dramatically increases the chemical palette of polymers that can form nanoparticles via emulsion polymerization.

A nonaqueous organic‐in‐fluorous emulsion applicable for polymerization using water‐sensitive catalysts is presented. With statistical biphasic copolymers based on poly(4‐hydroxystyrene) containing fluorinated and nonfluorinated alkyl side chains, emulsions of hydrocarbons dispersed in perfluorocarbons were stabilized. The addition of metallocenes, activated by methylalumoxane (MAO), enabled the polymerization of olefins inside this highly hydrophobic system. High molecular weight polyolefin nanoparticles ($\overline M _{\rm n}$ up to 450 000) of polyethylene and poly(propylene) were synthesized without supporting the catalyst and without reactor fouling. In this diffusion‐controlled process, the sizes of the particles were controlled by the reaction time and the ratio of the emulsifier to solvents.

The nonaqueous miniemulsion polymerization of liquid propene using highly water sensitive metallocene catalysts is presented. In the emulsion perfluoromethylcyclohexane is applied as continuous phase in which the monomer is polymerized to high molecular weights. The droplets are stabilized by specially designed of hydrocarbon/perfluorinated block copolymers. This technique offers the possibility to generate polyolefin nanoparticles with a narrow size distribution and diameters below 100 nm. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Nano‐sized latex support in metallocene polymerization is known to be able to avoid fuming or leaching and leads to a powder‐like and well‐processable polymer. Focus has been put on the fragmentation behaviour of the particles, a key parameter to morphology control. To study the different behaviour of the new systems as classical inorganic supported metallocenes, e.g. SiO2, a wide range of analytical methods were applied. Fluorescence microscopy, polymerization videomicroscopy, as well as kinetic studies led to a better understanding of the process. The performance of the supports was approved by several phenoxy‐imine type catalysts (“FI‐Catalyst”), which were combined with a tailored latex support. Ultra high molecular weight polyethylene (UHMWPE) was synthesized without any reactor fouling thereby. A different approach towards the metallocene catalyzed olefin polymerization is also presented. Based on emulsion polymerization, it enables very good control over product morphology. The completely hydrophobic system consists of perfluorinated solvent as a continuous phase and a hydrocarbon solvent as a dispersed phase. In contrast to the already existing water based emulsion polymerization of olefins, very high molecular weights are achieved.

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