Emulsion templating within water-in-oil emulsions is a well-known method for synthesizing hydrophobic porous polymers, while emulsion templating within oil-in-water (o/w) emulsions has recently been used to synthesize high-porosity hydrogel monoliths. The hydrogels templated within o/w emulsions exhibited amplified water uptake, enhanced sensitivity to local environment changes, and higher mechanical robustness compared to the same hydrogels that were not emulsion-templated. The main drawback to templating within o/w emulsions is the need to remove the large amount of internal phase, most often an organic solvent, following synthesis. Since the solvent is usually removed using a vacuum process, it is often dispersed in the atmosphere, or at best, collected in a container for organic waste. Therefore, it would be highly advantageous to develop green, environmentally friendly methods of synthesizing such high-porosity, emulsion-templated hydrogel monoliths.<br/>In this work, porous hydrogels were synthesized within solvent-free water-in-water (w/w) emulsions. A w/w emulsion can be formed by mixing an aqueous solution of poly(ethylene glycol) (PEG) (external phase) with an aqueous solution of a polysaccharide (internal phase). Here, w/w emulsion-templated hydrogels were synthesized through the free radical polymerization of monomers added to the PEG solution in that comprised the emulsion’s external phase. The monomers included a temperature-sensitive macromer (a methacrylated block copolymer with PEG endblocks and a poly(propylene oxide) midblock), a temperature-sensitive monomer (<i>N</i>-isopropylacrylamide), and a strongly hydrophilic monomer (2-acrylamido-2-methylpropane sulfonic acid). The resulting macroporous hydrogel monoliths exhibited densities ranging from 0.1 to 0.2 g/cc. The water uptakes of these hydrogels were tens of grams per gram polymer.

Porous hydrogels templated within water-in-water emulsions

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