Closed-cell and open-cell porous polymers from ionomer-stabilized high internal phase emulsions†
We firstly present a strategy that enables fabrication of both closed-cell and open-cell porous polymers (polyHIPEs) from high internal phase emulsions (HIPEs) stabilized with an ionomer, namely sulfonated polystyrene (SPS). Closed-cell polyHIPEs (St-polyHIPEs) were formed with styrene as the continuous phase in “parent” HIPEs whereas open-cell polyHIPEs (BA-polyHIPEs) were obtained with butyl acrylate as the continuous phase. The average diameters of pores in closed-cell St-polyHIPEs are 91.6 and 68.9 to 42.7 μm corresponding to the increase of the dispersed phase from 75 and 80 to 83 vol% in “parent” HIPEs, respectively. The surface of these closed pores is rough with scars, and the average number of scars per pore increases from 1.6 to 5.3 with increasing the ionomer concentration from 0.2 to 1.5%. The average sizes of both pores and windows in open-cell BA-polyHIPEs increase with the increasing content of the dispersed phase. The average diameters are 39.5, 48.5 and 65.3 μm for pores and 5.3, 7.8 and 13.4 μm for windows, corresponding to 75, 80 and 83 vol% of the dispersed phase in “parent” HIPEs. Amphiphilicity of these polyHIPEs can be reversibly and simply tuned by dipping them into solutions with different pH values, demonstrating that the ionomer is not removed during the purification. Ionomer-stabilized HIPEs provide a new approach for control over the size and interconnectivity of pores as well as the surface roughness and amphiphilicity of resultant porous polymers.