Polymer-Network Toughening and Highly Sensitive Mechanochromism via a Dynamic Covalent Mechanophore and a Multinetwork Strategy

Abstract

Multinetwork (MN) elastomers exhibit outstanding mechanical properties that arise from the sacrificial first network (FN). Here, we report the mechanical and mechanochromic properties of an MN elastomer with a difluorenylsuccinonitrile (DFSN) moiety incorporated into the cross-linking points of its FN. DFSN is a mechanochromophore that affords stable, pink radical intermediates upon exposure to mechanical stimuli. We distinctly demonstrated that the replacement of a conventional cross-linker by a weaker cross-linker does have a direct effect on the stress–strain behavior of elastomers to improve fracture toughness. The toughening mechanism of the DFSN-containing MN elastomers was revealed through a highly sensitive and quantitative analysis of the mechanically activated stable radicals by electron paramagnetic resonance spectroscopy. We also clarified that the MN strategy is an effective technique to achieve high activation of the mechanophores at a lower threshold strain.