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Utilization of Block Copolymers as Ultrafiltration Membranes

William A. Phillip1, Mark Amendt2, Brandon O'Neill3, Marc A. Hillmyer2, and Edward L. Cussler4. (1) Chemical Engineering & Materials Science, University of Minnesota, 421 Washington Ave SE, 151 Amundson Hall, Minneapolis, MN 55455, (2) Department of Chemistry, University of Minnesota, 421 Washington Avenue SE, Minnesota, MN, (3) Department of Chemical Engineering and Material Science, University o Minnesota, Los Angeles, MN 55455-5162, (4) Chemical Engineering and Materials Science, University of Minnesota, 151 Amundson Hall, 421 Washington Ave. SE, Minneapolis, MN 55455

Ultrafiltration membranes made by phase inversion are the current standard because of high fluxes, strong mechanical integrity and low cost. However, the broad distribution of pore sizes in these membranes is implicated in fouling. New ultrafiltration membranes should posses a narrower pore size distribution than current phase inversion membranes. Membranes made from block copolymers are an alternative because the copolymers can self assemble into pores on a nanometer scale. These pores are nearly monodisperse. Unfortunately, the porous copolymer membranes have lacked mechanical robustness.

Our work combines polymerization-induced phase separation and a "doubly reactive" block copolymer to make robust nanoporous membranes with a well defined pore structure. Gas and liquid transport measurements confirm the pore structure spans the films. Transport across these films agrees with predictions based on BET and SAXS so macroscopic cracks do not dominate transport. The demonstrated molecular weight cut-off of dextrans is significantly sharper for our films than a commercial membrane said to have a similar cut-off. Fouling studies will determine if further development of these materials is warranted.