Organic solvent reverse osmosis using CuAAC-crosslinked molecularly-mixed composite membranes

Molecularly-mixed composite membranes (MMCMs) incorporating amorphous scrambled porous organic cages (ASPOCs) are a rapidly emerging membrane class that are characterized by the formation of a solid solution due to a high degree of homogeneity that is not observed in other classes of polymer-particle composites. Molecular-level mixing overcomes many of the performance/processing issues typically encountered with two phase composite materials. However, chemical stabilization of the polymer matrix can deactivate the ASPOC cages. Here, we illustrate an alternative method of crosslinking Matrimid® in MMCMs using the copper catalyzed azide alkyne cycloaddition (CuAAC) click reaction. We fabricated thin film composite membranes and benchmarked them in a crossflow permeation system with standard styrene oligomers dissolved in a variety of organic solvents as well as an exemplar organic solvent reverse osmosis separation. We found that the presence of ASPOC increased both permeance and styrene dimer separation factor by up to 79% and 154%, respectively, over crosslinked Matrimid depending on the solvent, although the separation factor decreased at higher ASPOC loadings. The crosslinked MMCMs were challenged with a solvent-solvent separation in an organic solvent reverse osmosis modality and were able to effectively purify toluene from triisopropylbenzene. This work provides experimental observations needed to understand the mass transport processes occurring in MMCMs and highlights their separation performance and scale-up potential.