Mechanical bonds in polymer backbones: Does more mean better?

Abstract

Mechanical interlocked networks are an emerging class of network structures with exceptional mechanical properties. Their superior performance is primarily attributed to the mechanical bonds which combine excellent dynamics with strong stability. However, so far, a fundamental question remains: Does a higher mechanical bond content in polymer networks result in better performance? In this study, we designed polymer networks with varying mechanical bond contents in the backbone and found that an increase in content led to improved properties. Specifically, by adjusting the molar ratio of monomers containing mechanical bonds and comonomers, we synthesized three polymer networks with mechanical bond contents of 0%, 50% and 100%. Higher mechanical bond content led to enhanced mechanical properties, including elongation at break values of 37%, 225% and 380%, and toughness values of 0.17, 1.59 and 3.59 MJ/m3, respectively. Mechanistic studies revealed that the motion of mechanical bonds under stress effectively dissipates energy and releases hidden chains, which is beneficial for the material’s toughness and elongation. The functionality of individual mechanical bonds is more effectively integrated and amplified within a polymer backbone with higher mechanical bond content, resulting in better mechanical properties.