Dynamic bond exchange for accelerated and selective transport in polymer networks

Polymer networks with dynamic covalent bonds have been investigated for their viscoelastic properties and reprocessability. Here, the role of bond exchange on transport of small molecules is discussed. Experiments on neutral organic dyes reveal that bond exchange on comparable time scales to the diffusive hopping time of the penetrant can accelerate diffusion coefficients by orders of magnitude compared to permanent networks or slow exchanging dynamic networks. In particular, the enhancement grows when approaching the glassy state. The roles of segmental dynamics, bond exchange, and mesh size are discussed in terms of their relative importance at different temperatures. The impact of reversible penetrant-dynamic bond interactions is also found to be substantial in providing selectivity of similar sized penetrants. Finally, ion transport is shown to impact the exchange rate of various dynamic bonds and lead to distinct trade-offs in modulus, conductivity, and transference number in network electrolytes. Ions selectively partition to the dynamic bond or polymer backbone depending on the choice of chemistries. Dynamic covalent bonds are a key design parameter for controlling transport and selectivity in polymers for membranes and energy storage.