Polymerization of high internal phase emulsions

The dispersed phase of high internal phase emulsions may also be used to prepare polymeric materials in this case, conversion of monomer dispersed droplets to polymer results in latexes or particulates. 

Polymeric foams, called polyHIPE , has been developed by Unilever researchers5. The production of these porous materials was based on the polymerisation of high internal phase emulsion (HIPE)6. The system is composed of two phases an organic phase -called the continuous phase- containing the monomers and a suitable amount of emulsifier and an aqueous phase -called the dispersed phase- containing the radical initiator (scheme 1). 

A highly porous polymeric foam can be prepared through emulsion templating by polymerizing the continuous phase of high internal phase emulsions [150], A maleimide-terminated aryl ether sulfone oligomer was copolymerized with divinylbenzene in the continuous phase, using a mixed surfactants system, cetyltrimethylammonium bromide, dodecylbenzene-sulfonic acid sodium salt, and a peroxide initiator. The polymers show a CO2 adsorption and improved mechanical properties. The materials exhibit an open cell and a secondary pore structure with surface areas of a 400 m g ... 

Emulsion-templated highly porous PolyHIPE monoliths These are initiated from high internal phase liquid emulsions and polymerized (see the review by Silber-stein [42]). In general, the main porosity of High Internal Phase Emulsions (HIRES) lies in the micrometer size range, but HIRES may show a multiscale porosity with one distribution down to some tens of nanometers. 

A recent aproach to microporous foams involves the polymerization of high internal-phase water in oil emulsions (130). These flexible, hydrophilic open-celled foams are suitable for absorption of aqueous fluids and are being... 

Functionalized microporous polymers (with a superimposed nanostructure in the form of nanopores within the walls of the micropores) have been prepared through a high internal phase emulsion (HIPE) polymerization route.These polymers (known as PolyHIPE Polymers, PHP) were subsequently metallized by solution deposition followed by heat treatment. 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

The methods presented so far involve the use of polymers, either dissolved in a solvent or in a solid state. An alternative approach makes use of a water-in-oU emulsion, wherein the monomer is dissolved in the organic continuous phase. The monomer is then allowed to polymerize and cross-link around aqueous droplets. Depending on the physical conditions of the emulsion, adjacent emulsion droplets can be interconnected. This allows the removal of the aqueous phase via vacuum drying. Internal phase emulsions are classified as medium internal phase emulsions (MIPEs), with the fraction of the aqueous phase in the range 40—74%, or as high internal phase emulsions (HIPEs), with a volume fraction >74%. Scaffolds prepared via HIPEs had... 

Benicewicz, B. C., Duke, J. R., Hoisington, M. A., and Langlois, D. A., 1998, High temperature properties of poly(styreneco-alkylmaleimide) foams prepared by high internal phase emulsion polymerization. Polymer 39 4369 378. 

The high internal phase emulsion (HIPE) foams are currently of interest because of their low density, small cell size and high open cell content. A number of HIPE foams applications were reported, including, polymeric membranes, ion exchange resin [16-18] and absorbents. 

J.S. Choi, C. Chul and S.J. Lee. Effect of Rubber on Microcellular Stmctures from High Internal Phase Emulsion Polymerization Macromolecular Research, Vol. 11, No. 2, pp 104-109 (2003). 

A high internal phase liquid-liquid emulsion (HIPE) is one where the internal or dispersed phase droplets occupy >74% of the total volume of the emulsion. At this point the droplets contact each other and beyond this volume % the droplets are forced into distorted polyhedra. If for example styrene and divinylbenzene are employed as the continuous phase and water droplets dispersed in this oil phase using a suitable surfactant to form a HIPE, the comonomers can be polymerized to form a poly(styrene-divinylbenzene) polyHIPE. Typically the water droplets are... 

Fig. 2. Emulsion-templated crosslinked poly(acrylamide) materials synthesized by polymerization of a high internal phase C02-in-water emulsion (C/W HIPE). (a) SEM image of sectioned material, (b) Confocal image of same material, obtained by filling the pore structure with a solution of fluorescent dye. As such (a) shows the walls of the material while (b) show the holes formed by templating the SCCO2 emulsion droplets. Both images = 230 iJim X 230 jjim. Ratio of C02/aqueous phase = 80 20 (v/v). Pore volume = 3.9 cm /g. Average pore diameter = 3.9 jjim. Reprinted with permission copyright 2001 WILEY VCH Verlag GmbH Co. [28].

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