Orthogonal Dynamic Bonds Generate Multiple Relaxation Processes in Soft Networks with Different Polymer Architecture

Polymer with tunable viscoelasticity is of paramount importance in damping applications. For example, polymers with hierarchical relaxation processes facilitate energy dissipation over a wide frequency range. However, it is still challenging for the rational design of polymer networks with such properties, as many competing factors affect dynamics. Here, mixed orthogonal dynamic bonds with 10,000 times different exchange kinetics were introduced into PDMS with both pendant and telechelic architecture to understand how the network connectivity and bond exchange mechanisms determine the overall relaxation spectra. A hydrogen-bonding group and a vitrimeric imine crosslinker are combined into the same network, and well-resolved multiple relaxation processes are observed with both pendant and telechelic PDMS architecture. Two modes are not observed when mixed bonds share an exchange mechanism. With both orthogonal dynamic bonds, excellent damping and improved mechanical properties are observed and strongly correlated with the complex viscoelasticity. In addition, hydrogen-bond exchange can result in two adjacent relaxation processes depending on the network architecture. This work provides molecular insights for the predictive design of hierarchical dynamics in soft materials.