PolyHIPEs are porous emulsion-templated polymers that are usually synthesized using free radical polymerization within surfactant-stabilized water-in-oil high internal phase emulsions (HIPEs) [1,2]. High-porosity hydrogel polyHIPEs (HG-PHs), based on ionic and/or non-ionic monomers and crosslinked with N,N'-methylenebisacrylamide, were synthesized within oil-in-water HIPEs [3-6]. The extraordinary water absorbency of the HG-PHs was ascribed to a hydrogel-swelling-driven void expansion mechanism (see Figure). The water uptakes in the ionic HG-PHs were pH-responsive, while those in the HG-PHs based on N-isopropylacrylamide were temperature-responsive. Mechanically robust HG-PHs based on 2-acrylamido-2-methyl-propansulfonic acid exhibited unusually high water and artificial urine uptakes. The highly accessible sulfonic acid groups produced a high ion exchange capacity and rapid dye absorption. Doubly-crosslinked HG-PHs with reversible metal-coordination crosslinking were fabricated by adding FeCl3 to covalently crosslinked HG-PHs based on acrylamide and sodium acrylate. The metal-coordination crosslinking significantly enhanced the mechanical properties but did not affect the interconnected macroporous structures or the rapid water absorption. Shape memory behaviour resulted from imposing a temporary shape through double crosslinking and then recovering the original shape by removing the double crosslinking. Other HG-PHs exhibited an anti-polyelectrolyte effect (an increase in NaCl solution uptake with increasing concentration) and a dual-response uptake with pH (decreasing from 2 to 7, increasing from 7 to 10). This work clearly demonstrates that emulsion templating amplifies the magnitude of the hydrogel network’s response to the environment and accelerates its response.

Emulsion templated hydrogels: Superabsorbents, stimulus-responsive, double-crosslinking, and dual-response

255th National Meeting (2018)

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