Poly internal phase emulsions

The idea of the preparation of porous polymers from high internal phase emulsions had been reported prior to the publication of the PolyHIPE patent [128]. About twenty years previously, Bartl and von Bonin [148,149] described the polymerisation of water-insoluble vinyl monomers, such as styrene and methyl methacrylate, in w/o HIPEs, stabilised by styrene-ethyleneoxide graft copolymers. In this way, HIPEs of approximately 85% internal phase volume could be prepared. On polymerisation, solid, closed-cell monolithic polymers were obtained. Similarly, Riess and coworkers [150] had described the preparation of closed-cell porous polystyrene from HIPEs of water in styrene, stabilised by poly(styrene-ethyleneoxide) block copolymer surfactants, with internal phase volumes of up to 80%. 

Krajnc P, Leber N, Stefanec D, Kontrec S, and Podgomik A. Preparation and characterisation of poly(high internal phase emulsion) methacrylate monoliths and their application as separation media. J. Chromatogr. A 2005 1065 69-73. 

The structure of laboratory-made polyhigh internal phase emulsion (poly-HIPE) was successfully characterized by CPMAS, solid-state NMR experiments. 

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. 

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... 

Combination of rapid solvent extraction and evaporation was adopted to minimize drug loss and improve the encapsulation efficiency of neurotensin peptide. Neurotensin was encapsulated in poly-dl-lactic acid at high concentrations by the O/W emulsion solvent removal methods using an internal phase consisting of mixed solvent system. One of the solvents is water immiscible... 

The maximum internal phase ratio that can be attained without deforming the drop spherical shape depends on the drop size distribution. For monodispersed rigid spheres, the most dense tessellation is the hexagonal packing at about 74% of internal phase. As an example, for randomly settled monodispersed spheres it could be 65%. For very poly dispersed emulsions it might be higher than 90% (16). 

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].

The difunctional derivative DIAMA has also been used in emulsion polymerization (Figure 17) 30,231 enabling a significant reduction in particle size and narrower distribution compared to latexes prepared using monoflinctional BlocBuilder MA . Polystyrene-I -poly(n-butyl acrylate)-Zi-polystyrene triblock copolymers were made using the difunctional alkoxyamine, and allowed nanostmctured particles to be formed upon internal phase separation. A refined semibatch process shortened overall process time compared to earlier efforts. ... 

Maa and Hsu (75) reported the formation of nano-particles by the double-emulsion method (W/OAV), using methylene chloride as an organic solvent and poly(vinyl alcohol) (PVA) or human serum albumin (HSA) as a surfactant. Experimental parameters such as the preparation temperature, the solvent-evaporation method, the internal aqueous phase volume, the surfactant concentration, and the polymer molecular weight were investigated for particle size, the zeta potential, the residual surfactant percentage, and the poly-dispersity index. Preparation parameters leading to particles with well-defined characteristics such as an average size around 200 nm and a polydispersity index lower than 0.1 were identified. 

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