Influence of linker length and dynamic bond chemistry on enhanced diffusion in vitrimers

Polymer networks with dynamic covalent bonds can enhance the transport of penetrants through the bond exchange mechanisms, making them promising candidates for next-generation membranes. In this study, imine dynamic bonds in ethylene oxide networks were investigated for a broad range of linker lengths spanning mesh sizes above and comparable to the size of an organic penetrant. Mesh sizes were determined from shear rheology and glass transition by calorimetry. The diffusion coefficient of a large aromatic dye molecule was measured by fluorescence recovery after photobleaching as a function of mesh size and temperature. Permanent networks show up to a three orders of magnitude reduction in diffusion compared to the dynamic systems for the shortest linker lengths. Dynamic networks with mesh sizes greater than the dye diameter show a similar temperature dependence of the diffusion coefficient, while small mesh sizes exhibit massively hindered diffusion. For large mesh sizes, the permanent and dynamic networks show the same diffusion coefficient. These findings provide insights into the factors affecting penetrant transport in dense polymers and inspire the development of next-generation selective polymer membranes.