Roles of mesh size, segmental dynamic, glass transition temperature, and molecular structure on penetrant diffusion in dense vitrimers

We have systematically investigated how dynamic crosslinks can facilitate the transport of polyaromatic dye in the n-butyl acrylate networks. Two different boronic ester crosslinks with different bond exchange rates were compared to study the effect of bond exchange on penetrant diffusion. Diffusion of a large anisotropic fluorescent molecule was measured by fluorescence recovery after photobleaching (FRAP). The diffusion coefficients of the dye were normalized by mesh size and Tg/T, and in both cases diffusion is enhanced in the dynamic networks. Finally, we investigated the selective diffusion of two different dyes. These two penetrants have similar structure, but one of them could participate in reversible dynamic bonding with the dynamic crosslinks and the other could not. When the mesh size was smaller than the dye size, diffusion was abruptly restricted for the non-reactive dye, while the reactive dye was able to continue diffusion with a faster rate. Our results show that dynamic crosslinks can enhance penetrant diffusion and provide a route towards selective transport in polymer membranes.