Macroporous poly(ionic liquid) and poly(acrylamide) monoliths from CO2-in-water emulsion templates stabilized by sugar-based surfactants

Abstract

Highly interconnected poly(acrylamide) (PAM) and poly(vinylimidazolium) (PVIm) porous monoliths were templated by carbon dioxide-in-water (CO₂/W) high internal phase emulsions (HIPEs), a toxic-solvent free process. A range of sugar-based fluorinated surfactants prepared by chemoenzymatic synthesis were used as emulsifiers. Both the concentration and the structure of the surfactants, especially the length of their CO₂-philic part and of their spacer between the sugar head and the tail, were found to strongly affect the cellular structure and morphology of the PAM polyHIPEs, i.e. the size of pores and cells. A mannose derivative bearing a chain ranging from 6 to 10 perfluorinated carbons and a long spacer emerged as the best stabilizer, leading to a porous monolith with average pores and cell sizes (about 2.6 μm and 5–10 μm, respectively) among the lowest reported for polyHIPEs produced from CO₂/W emulsions. The same template then served for the preparation of the first macroporous poly(ionic liquid) (PIL) polyHIPE by using 1-vinyl-3-ethylimidazolium bromide as the monomer. Shrinkage of the final material was prevented by adjusting the divinylimidazolium crosslinker content. The resulting low density polyHIPE exhibits small spherical cells (∼5 μm) connected by numerous small pores (∼2 μm), confirming that the CO₂/W HIPE templating methodology based on fluorinated glycosurfactants is a technique of choice for the preparation of macroporous PILs.