Ionically Cross-Linked Triblock Copolymer Hydrogels with High Strength

Abstract

High strength hydrogels were made by ionically cross-linking the polyelectrolyte midblock of a self-assembled, amphiphilic triblock copolymer network. The polymer backbone consisted of glassy, spherical domains of poly(methyl methacrylate) (PMMA) end blocks bridged by solvated poly(methacrylic acid) (PMAA) midblocks, whose assembly was induced by vapor phase solvent exchange. Ionic cross-linking was achieved by submersion of polymer gels into pH-buffered solutions of divalent acetates (Zn, Ca, Ni, Co, Cu). Consequent mechanical characterization by tensile and indentation testing methods revealed a dependence of mechanical behavior on ion absorption, pH, and cation identity with orders of magnitude increases in Young’s modulus between cross-linked and noncross-linked states. These materials exhibit a degree of reversible energy dissipation with mechanical responses reminiscent of tough double network hydrogels and fracture stresses up to ∼1 MPa.