Resolving hyperelasticity-adhesiveness conflict in polymer networks by in-situ constructing mechanical heterogeneities

In polymeric materials, hyperelasticity (i.e., low hysteresis) and strong adhesion are often required but difficult to achieve simultaneously. Herein, we propose a design principle of polymer networks that are hyperelastic yet adhesive by rationalizing mechanical heterogeneities. The heterogeneous networks comprise a viscoelastic adhesive surface and a hyperelastic non-adhesive bulk. The former has a stiffness much smaller than that of the latter. We synthesize the networks by harnessing the oxygen inhibition mechanism, construct a polymerization phase diagram by reconciling the kinetics of polymerization and radical quenching of oxygen, and establish a power law criterion for the transition from a viscoelastic adhesive network to a hyperelastic adhesive network. We illustrate the principle with heterogeneous poly(butyl acrylate-co-acrylic acid) networks, achieving hysteresis < 5% and adhesion energy > 300 J/m2. We show that the adhesion energy-thickness relation of hyperelastic adhesive polymer networks is nonlinear below a transition thickness. Hyperelastic and adhesive stretchable materials potentialize high-cycle and fatigue-resistant soft human-machine interfaces and beyond.