Molecular design rules for imparting multiple damping modes in dynamic covalent polymer networks

Imparting multiple, distinct dynamic processes at precise timescales in polymers is a grand challenge in soft materials design with implications for applications including electrolytes, adhesives, tissue engineering, and additive manufacturing. Many competing factors including the polymer architecture, molecular weight, backbone chemistry, and presence of solvent affect the local and global dynamics, and in many cases are interrelated. One approach to imparting distinct dynamic processes is through the incorporation of dynamic bonds with widely varying kinetics of bond exchange. Here, statistically crosslinked polymer networks are synthesized with mixed fast and slow dynamic bonds with four orders of magnitude different exchange kinetics. Oscillatory shear rheology shows that the single component networks (either fast or slow) exhibit a single relaxation peak, while mixing fast and slow crosslinkers in one network produces two peaks in the relaxation spectrum. This is in stark contrast to telechelic networks with the same mixture of dynamic bonds where only one mixed mode is observed, and here we develop the molecular design rules necessary to have each dynamic bond contribute a distinct relaxation mode. By controlling the polymer architecture and difference in the number of dynamic bonds per chain, we have elucidated the role of network architecture on imparting multimodal behavior in dynamic networks. A highly tunable and recyclable material has been developed with control of rubbery plateau modulus (through crosslink density), relaxation peak locations and ratio (through crosslinker selection and molar fractions), and tan δ (through the relationships of the rubbery plateau and relaxation peak locations).