Polymerization of hydrophilic monomers

Nanogels made up of various intramolecularly cross-linked macromolecules have been prepared simply by performing the polymerization of hydrophilic monomers solubilized in the micellar core of reversed micelles, and they represent distinct macromolecular species from those obtained in bulk [191,240]. 

Organic compounds such as polystyrene latexes were also used as substrates for the surface-initiated radical polymerizaiton.248 Reactive C—Br bonds (S-12) were introduced at the surface via radical emulsion copolymerization of styrene and 2-(2-bromopro-pionyloxy) ethyl methacrylate in the presence of divinylbenzene under selected conditions. The surface-initiated polymerization of hydrophilic monomers such as FM-3 and FM-6 resulted in hydrophilic shell and hydrophobic core latexes. 

Another possibility for altering a is a complete change of the dispersion medium. Besides water other classes of suitable liquids are alkanes or perfluorocar-bon fluids. By using such materials a drastic decrease in / can be achieved (cf. Table 8.4) when compared to water (/w = 72.8 mN m ). Indeed, it is the state of the art (also in larger-scale technical processes) to use certain petroleum fractions as continuous phases for the polymerization of hydrophilic monomers (so-called inverse heterophase polymerizations) to prepare, for instance flocculants for waste-water treatment or as aids for paper production (14). The large-scale application of perfluorocarbon fluids, however, is restricted... 

The invase (wata-in-oU w/o) emulsion methods involve polymerization of hydrophilic monomers in the presence of cross-linker in aqueous droplets. In such systems, the monomer or the aqueous monoma solution is emulsified in a continuous hydrophobic phase. The polymerization can be initiated either from the droplet or from the continuous phase. Using aoss-finking agent(s) in the monoma mixture leads to the formation of miaogel NPs afta polymerization, keeping their identity after transferring them into water as continuous phase. 

Inversion emulsion polymerization involves the dispersion and then polymerization of hydrophilic monomers, normally in aqueous solution, in a nonaque-ous continuous phase. The emulsifier systems primarily based on the steric stabilization mechanism (see Section 1.3.3) are quite different from those of the more conventional oil-in-water emulsion polymerization processes. This is simply because the electrostatic stabilization mechanism (see Section 1.3.2) is not effective in stabilizing inverse emulsion polymerization comprising an aqueous disperse phase and a nonaqueous continuous phase with a very low dielectric constant. The unique anionic surfactant bis(2-ethylhexyl) sulfosuc-cinate (trade name Aerosol OT) that can be dissolved in both oil and water... 

A modification of the micro-emulsion polymerization is pol5meriza-tion in reverse micelles, called inversed or micellar polymerization. This issue concerns the polymerization of hydrophilic monomers, from which one obtains the water-soluble pol miers. Therefore, as the phase diffuser mostly hydrocarbons such as isooctane, heptane, benzene or toluene are used. 

Figure 3.2 Schematic representation of (a) oil-in-water (O/W) emulsion polymerization m the presence of hydrophilic clay platelets and (b) water-in-oil (W/O) inverse emulsion polymerization of hydrophilic monomer with hydrophilic clay which, hypothetically, may lead to clay encapsulated inside the latex particles.

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