High porosity, responsive hydrogel copolymers from emulsion templating

Hydrogels, three-dimensional hydrophilic polymer network structures, can absorb many times their dry weight in water. PolyHIPEs are highly porous polymers synthesized within high internal phase emulsions (HIPEs). Here, the water uptakes in novel hydrogel polyHIPE copolymers of hydroxyethyl methacrylate (HEMA, a non-ionic monomer) and methacrylic acid (MAA, an ionic monomer) were investigated. The PHEMA-based polyHIPE had a density of 0.14 g cm(-3), void diameters of 50-100 mu m and a void-dominated Fickian water uptake of around 10.4 g g(-1). The polyHIPE density increased, and the porous structure became less polyHIPE-like, with increasing MAA content, reflecting a reduction in the stability of the HIPE. The water uptake increased with increasing pH for all the copolymers and the water absorption mechanism changed from Fickian at pH 2 to anomalous, dominantly case II, at pH 10. The maximum uptake of 18.2 g g(-1) at pH 10, for a HEMA to MAA mass ratio of 1/1, was ascribed to hydrogel-swelling-driven void expansion. The hydrogel's absorptive and responsive properties were amplified by the polyHIPE's porous structure. These results demonstrate that the compositions of hydrogel polyHIPE copolymers can be designed to enhance their water uptake. (c) 2015 Society of Chemical Industry