This paper aims to unravel the complex microstructure of tough, �double network� (DN) hydrogels synthesized by free-radical polymerization of a monomer within a highly crosslinked polyelectrolyte hydrogel and to discuss the key topological factor for toughness enhancement. Fourier transform infrared (FTIR) characterization of a hydrogel synthesized from 3-sulfopropyl acrylate potassium salt (SAPS) and 2-hydroxyethyl acrylate (HEA) demonstrated that polymer chains synthesized during the second polymerization step are grafted to the skeleton of the polyelectrolyte network. Uniaxial tensile tests performed on hydrogels synthesized from SAPS and acrylamide (AAm) indicate that linear and nonlinear polymerization of a second monomer within a network without grafting to the first network, i.e., forming a semi-interpenetrating or interpenetrating network, does not produce a tough hydrogel. In effect, grafting high molecular weight polymer chains synthesized during the second polymerization step to a first, highly crosslinked polyelectrolyte network with residual unsaturation is indispensible for achieving toughness. Moreover, the concentration of the grafted chains is a crucial factor in determining the mechanical behavior of the hydrogel.

Deconstructing double network hydrogels: The importance of grafted chains for achieving toughness

248th National Meeting (2014)

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