Multifunctional Membranes

Marc A. Hillmyer of the University of Minnesota, Twin Cities, unveiled his group’s “reaction-induced self-assembly method” as a modular approach for engineering multifunctional, multicomponent block polymers to serve as nanoporous membranes for drug delivery, water filtration, and separations applications. In commercially available ultrafiltration membranes, there’s a trade-off between membrane selectivity and liquid permeability—highly selective membranes have low permeability and vice versa, Hillmyer explained. To overcome this problem, Hillmyer’s group has been using the new method to prepare membranes that combine high porosity and narrow pore-size distributions with tunable chemical and mechanical properties. In one example, Hillmyer and coworkers made a membrane from a polymer containing a reactive polystyrene copolymer block (blue), a poly(N-isopropylacrylamide) block (PNIPAM, red), and a poly(lactide) block (PLA, green). In the presence of a metathesis catalyst, the reactive block cross-links with polymerizing dicyclopentadiene (blue diamonds) to create the membrane matrix. Etching out the PLA creates pores lined with thermally responsive and reactive PNIPAM. The resulting tough nanoporous material can be formed as thin sheets and holds potential as a highly selective, highly permeable water-filtration membrane, Hillmyer said.