Design of Mechanochromic Elastomers Based on Dynamic Covalent Chemistry

Abstract

Mechanochromism is color change phenomenon in response to mechanical stress. The importance of mechanochromic polymers has increased due to the application to stress detection and damage prediction of the polymeric materials. In the present review, some characteristic approaches to mechanochromic polymers are introduced. In particular, mechanochromic elastomers utilizing polymer reactions based on dynamic covalent chemistry are described in detail. Diarylbibenzofuranone (DABBF), which can undergo homolytic cleavage of the central C-C bond by mechanical force to form relatively stable blue-colored radicals, was used as a mechanochromophore because the cleaved radicals could be evaluated quantitatively using electron paramagnetic resonance measurements. Well-defined linear and star polymers with a mechanochromophore functionality at the center of each polymer structure were designed to prepare mechanoresponsive materials with high sensitivity and demonstrate the relationship between polymer architecture and mechanoresponsiveness in the bulk state. Two types of mechanochromic elastomers were prepared; one is segmented polyurethanes and the other is polymer/silica nanocomposite elastomers. The segmented polyurethanes were synthesized by polyaddition, whereas the polymer/silica nanocomposite elastomers were prepared by sol-gel method. The mechanochromic properties of both elastomers are described.