Tough Double-Network Gels and Elastomers from the Nonprestretched First Network.

Double-network (DN) gels and elastomers, which consist of two (or more) rubbery polymer networks with contrasting physical properties, have received significant attention as they are extremely tough soft materials. The first network of tough DN materials should be more brittle and weaker than the second network. In this paper, we re-examined the structural requirements of the covalently cross-linked first network of tough DN materials and established a nonprestretching strategy. While prestretching of network strands has been considered necessary for the preparation of the brittle and weak first network, we found that a nonprestretched network having a short strand length and low strand density can be used as the brittle and weak first network for preparation of both tough DN gels and elastomers. This work can further expand the chemical and mechanical diversity of DN materials.