(498c) Stiffening Polymer Brush Membranes for Enhanced Organic Solvent Nanofiltration Selectivity

Polymer membranes offer several advantages such as ease of synthesis and low cost. However, commercial application of these membranes is limited to separations that feature an order of magnitude difference in size between constituents. This can be attributed to inherent limitations of polymer materials such as pore flexibility and a log normal pore size distribution. As a consequence, polymeric membranes have seldom been employed industrially for the separation of organic solvents that require separation of molecules similar in size. A new class of polymer brush membranes are synthesized and tested for the separation of organics currently not likely with the majority of membranes made by phase inversion or interfacial polymerization.

This work overcomes fundamental limitations of polymers by stiffening brush membranes and stabilizing the pores. Pyrolyzing polymer membranes have shown enhanced selectivity for hydrocarbon separation and increased stiffness was implicated qualitatively¹. A commercial support (crosslinked polyimide) is modified by graft polymerization of a primary amine monomer using a novel and green technique: Single Electron Transfer- Living Radical Polymerization (SET-LRP). This is followed by crosslinking and thus stiffening these brush membranes using aliphatic (itaconic) and aromatic (trimesic) acids. The synthesized membranes show selectivity for (i) toluene- triisopropyl benzene (TIPB) and (ii) methanol- toluene separation and this selectivity is positively correlated with brush rigidity (Fig. 1) for the first time to the best of our knowledge. The membranes are further characterized by ATR-FTIR, zeta potential, AFM and XPS in addition to the investigation of mechanism of transport using a series of pure solvents. This new class of tunable and scalable membranes offers a way to replace energy intensive distillation and low capacity adsorption separation in the field of solvent purification.

(1) Ma, Y.; Jue, M. L.; Zhang, F.; Mathias, R.; Jang, H. Y.; Lively, R. P. Creation of Well-Defined “Mid-Sized” Micropores in Carbon Molecular Sieve Membranes. Angewandte Chemie International Edition 2019, 58 (38), 13259–13265.