PolyHIPEs — Porous Polymers from High Internal Phase Emulsions

A large variety of porous polymers, generally known as polyHIPEs, have been synthesized using high internal phase emulsions (HIPEs) as templates for the porous structure. HIPEs are formed by mixing two immiscible liquids in the presence of an emulsifier, usually a surfactant, such that the internal phase content is more than 74 %. PolyHIPE are synthesized through the polymerization of monomers in the external phase. The internal phase can be evacuated through holes that develop in the polymer walls, yielding a porous polymer. Hydrophobic polymers can be synthesized within water-in-oil emulsions and hydrophilic polymers can be synthesized within oil-in-water emulsions. The types of materials synthesized include copolymers, interpenetrating polymer networks, biodegradable materials, organic-inorganic hybrids that can be pyrolyzed to porous inorganics, nanocomposites, and hydrophobic-hydrophilic bicontinuous polymers. The large number of methods available to functionalize polyHIPEs have enhanced their utility for such applications as chemical synthesis, chromatography, ion exchange, separation, sensing, tissue engineering, and controlled drug delivery, to name but a few. This article describes HIPE formation and stability, polyHIPE synthesis and functionalization, polyHIPE morphology, polyHIPE properties, a variety of different polyHIPE-based materials, and polyHIPE applications. Keywords: polyHIPE; porous; emulsion templating; emulsifier; synthesis