Insights into the Role of Hydrogen Bonds on the Mechanical Properties of Polymer Networks

The incorporation of weak and reversible dynamic bonds is a key strategy for enhancing the mechanical properties of polymers. However, the quantitative relationship between the molecular characteristics of dynamic bonds and the resultant macroscopic mechanical properties has not been elucidated fully. Here, we systematically investigated the effect of hydrogen bonds (H-bonds) on the mechanical properties of polymer networks. Three types of H-bonding groups were homogeneously introduced into identical polymer networks with a nearly ideal structure. The number density and thermodynamic characteristics, that is, binding energy of H-bonds, controlled properties such as stiffness and stretchability of polymer networks. On the other hand, the activation energy of chain motion and the rate of recovery after mechanical loading depended on the kinetic aspects of the H-bonds, that is, the energy barriers to dissociation and re-association. These findings provide a principle for selecting appropriate dynamic bonds to design materials with desired properties.