Force-Responsive Polyethylene with Quantifiable Visualized Color Changing

Mechanochromic polymeric materials have enormous potential applications in stress-sensing and damage detection. These types of polymers including poly(methyl acrylate), poly(methyl methacrylate), poly(urethane), and poly(ε-caprolactone) have been achieved through various methods, such as postfunctional reaction, free radical polymerization, polycondensation, and ring-opening polymerization. However, coordination polymerization to incorporate mechanochromophores into semicrystalline polyethylene, an extremely important and common plastic, is rare. Herein, we report functionalized polyethylene materials via coordination copolymerization of ethylene and a well-designed comonomer C4-ABF containing the mechanochromic group catalyzed by phosphine–sulfonate palladium catalysts and the following cross-linking reaction. These copolymer materials exhibit a visible color change under force stimulus, transferring the force signal to the color signal. The red–green–blue (RGB) color analysis method is adapted to investigate the relationship between stress–strain and color change. It is noted that the blue channel intensity has a positive correlation with Hencky stress.