One-pot emulsion-templated synthesis of an elastomer-filled hydrogel framework

Sulfonated polymers are of interest as semipermeable ion-selective materials for membrane applications and as conductive materials for antistatic, electrode, and fuel cell applications. An innovative "one-pot" synthesis route was developed to produce relatively flexible systems containing a cross-linked polyacrylate elastomer within a continuous sulfonated hydrogel network. This synthesis route was based on the formation of a high internal phase emulsion (HIPE) containing an aqueous solution of styrenesulfonate and a cross-linking comonomer in the external phase and containing 2-ethylhexyl acrylate and a cross-linking comonomer in the internal phase. Both emulsifier-stabilized HIPEs and emulsifier-free polymer-nanoparticle-stabilized Pickering HIPEs were investigated using this route. A "three-step" route consisting of sulfonating a cross-linked polystyrene (xPS)-based polyHIPE in sulfuric acid and then polymerizing 2-ethylhexyl acrylate and a cross-linking comonomer within the polyHIPE was used for comparison. The chemical composition, two-phase morphology, water absorption, and mechanical properties of these materials were investigated. Unexpectedly, the walls of the materials based on cross-linked poly(styrenesulfonate) (xPSS) were found to contain cross-linked poly(2-ethylhexyl acrylate) nanodomains. Water absorption per mass sulfonated polymer was significantly greater in the xPSS-based material synthesized within a nanoparticle-stabilized HIPE.