(538c) Cross-Linking of Matrimid/Porous Organic Cage Molecularly Mixed Composite Membranes Using Cycloaddition Click Chemistry

Individual molecules with intrinsic porosity, like amorphous scrambled porous organic cages (ASPOCs), have the potential to “change the game” when it comes to creating composite and hybrid materials. A particularly exciting potential application is to incorporate these materials into polymeric membranes to form molecularly mixed composite membranes (MMCMs). Since ASPOCs are individual molecules instead of continuous 3-dimensional structures like metal-organic frameworks or zeolites, they should be able to form a “solid solution” with the ASPOC uniformly dispersed throughout the membrane at a molecular level. This molecular-level mixing overcomes many of the performance/processing issues encountered with other composite materials. Due to small window sizes, ASPOCs should be able to distinguish between aggressive, small molecule organic solvents effectively. Cross-linked polyimides like Matrimid® are also thought to be appropriate for this application due to high chemical stability. Unfortunately, the normal diamine crosslinking process for polyimides would cause the degradation of the ASPOC molecules since they are bound by relatively weak imine bonds. Here we propose an alternative method of cross-linking Matrimid® in MMCMs using “click” chemistry, specifically the Huisgen azide-alkyne cycloaddition reaction. Importantly, the reaction does not involve species that will degrade the ASPOC. To test MMCM separation performance, we fabricate thin film composite membranes and test them in a crossflow permeation system with standard styrene oligomers dissolved in a variety of organic solvents. We find that the presence of ASPOC increases both permeance and styrene dimer separation factor up to a loading of 20 wt%. Even in THF, known to dissolve uncross-linked Matrimid, we measure permeances of 0.96 LMHBar and a dimer separation factor of 27.5 at 10 wt% ASPOC loading. The crosslinked MMCMs are also able to distinguish between toluene and triisopropylbenzene, suggesting their suitability for solvent-solvent class separations.