The significant role of enantiomeric excess of the monomer in binaphthalene-based polymer membranes

Numerous studies have been carried out to improve the membrane performance and stability of solvent-resistant nanofiltration membranes. This research aims at studying the influence of molecular structure on the membrane performance in a step-wise fashion, making it possible to specifically fine-tune membranes towards their application. For this purpose, a tunable binaphthalene di(acid chloride) is combined with several amine monomers. This choice of monomers allows to simultaneously study (1) the influence of the enantiomeric excess, since binaphthalenes show atropisomerism and (2) the influence of the number and position of the amine functionalities. By varying the amount and position of the amine functionalities relatively small changes in the filtration performance are observed. However, in case optically pure acyl chloride is used, the membrane performance excels independent of the amine used. The water and acetonitrile permeance of the optically pure membranes even doubles in comparison to the optically impure membranes, independent of the degree of e.e. (0, 25, 50 or 75 %e.e.), while maintaining a similar rejection. Hence, this study adds a polymer's enantiomeric excess to the toolbox of parameters that can be used to tailor membrane properties.