Tailoring the mechanical performance of highly permeable macroporous polymers synthesized via Pickering emulsion templating

Abstract

Highly interconnected macroporous polymers can be produced by the polymerization of high internal phase emulsions (HIPEs) with a dispersed phase exceeding 74 vol%. Until recently, it was thought that poly(merized)HIPEs with a maximum reported gas permeability of 0.46 D could only be produced by the polymerization of surfactant stabilized HIPE templates. However, highly permeable macroporous polymers with a gas permeability of up to 2.6 D were successfully prepared by adding small amounts of a non-ionic surfactant to pre-made Pickering emulsion templates; poor mechanical properties (crush strengths of ≤2.2 MPa) however limit the applicability of these materials. The mechanical properties were improved by altering the composition of the emulsion template. This involved using the flexible crosslinker polyethylene glycol dimethacrylate (PEGDMA), alongside other organic additives like divinylbenzene (DVB) and squalene in the organic phase. We also increased the material density by using medium internal phase emulsion (MIPE) templates and increased the surfactant concentration added to the pre-made Pickering-MIPEs. The resulting materials were characterized in terms of pore structure, gas permeability and mechanical performance. SEM images revealed pores of up to 1700 μm in diameter and interconnecting pore throats of up to 100 μm in diameter. The highest gas permeability and crush strength achieved were 0.92 ± 0.09 D and 5.6 ± 0.1 MPa, respectively, for a macroporous polymer synthesized from a Pickering-MIPE containing 50 : 40 : 10 (by volume) styrene, PEGDMA and DVB respectively, in the organic phase, to which 10 vol% Hypermer 2296 was added.