Nanoporous separation membranes from microphase-separating block copolymers

Nanoporous separation membranes from microphase-separating block copolymers

Jw

Conventional polymeric membranes based on standard polymers such as cross-linked aromatic polyamide for nanofiltration (applied to brackish water desalination or water softening) have reached their performance limits, and they have also insufficient chemical resistance against important oxidative disinfectants which makes the process more complicated. Significant improvements could be achieved if the random packing of segments like in classical amorphous polymers [1] would be replaced by controlled microphase-separated structures in “tailor-made” membrane polymers [2]. This work makes a contribution to the development of novel microphase-separated block copolymers to obtain “nanoporous” membranes with barrier pore diameters in the range between < 1 and ~2 nm.

This is realized by routes combining corresponding telechelic macromonomers (fluoride-terminated and hydroxyl-terminated, with different chain lengths) obtained by a molecular-weight controlled polycondensation according to Carothers´ equation and a subsequent second polycondensation step. The obtained poly(arylene ether sulfone) multiblock copolymers are then functionalized to create in a block-selective fashion cation- and anion-exchange polymers [3]. The focus is on anchoring anion-exchange groups on the main chain of these polymers because the knowledge about the potential of such materials for nanofiltration is much less explored than that about cation-exchange polymers. On the basis of the characterization of polymer films (SEM, AFM, TEM, DSC, SAXS, ion exchange capacity and swelling) and thin-film composite membranes obtained via evaporation-induced phase separation (flux and salt rejection), relationships between polymer synthesis and processing on the one hand, and obtained membrane structure and properties on the other hand will help to improve separation performance of nanoporous membranes by macromolecular design.

References

  1. D. G. Cahill, V. Freger, S. Y. Kwak, MRS Bulletin, 2008, 33, 27
  2. N. W. Li, M. D. Guiver, 2014, 47, 2175
  3. M. Kumar, M. Ulbricht, RSC Advances, 2013, 3, 12190
Funding: This work is funded by Evonik Industries AG.

Contact:
Prof. Dr. Mathias Ulbricht