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Tough Nanoporous Membranes with a 3-D pore structure

Recent research from the group of Professor Marc Hillmyer.

Controlled fabrication of nanoporous polymer membranes has attracted growing interest due to their applicability as catalyst supports, ultrafiltation membranes, or templates for the synthesis of other nanomaterials. It has been generally shown that self-assembled block copolymers comprising a non-degradable block (matrix) such as polystyrene (PS) and a chemically-etchable block such as polylactide (PLA) can be used to generate nanoporous materials upon removal of the sacrificial component. However, in most cases the nanoporous materials made by this route suffer from poor mechanical performance and limited chemical and thermal stability. While crosslinking the matrix material has shown promise in improving the thermal properties, the lack of toughness in these materials is still a significant issue.

Targeting novel nanoporous polymer membranes that are chemically, thermally and mechanically robust, graduate student Liang Chen working with Professor Marc Hillmyer integrated polydicyclopentadiene (polyDCPD), a strong thermosetting material prepared by Ring-Opening Metathesis Polymerization (ROMP), and PLA into thin polymeric films. By incorporating a "doubly" reactive block copolymer containing etchable PLA and ROMP-reactive PNS (see chemical structures below) during the ROMP of DCPD using Grubbs catalyst, Liang prepared a nanoscopically organized composite film. Removal of the PLA by treatment with aqueous base yielded a nanoporous membrane (average pore diameter of 17 nm) with a high porosity (40%), a large specific surface area (160 m2 g–1), and narrow pore size distribution. The resulting mesoporous polyDCPD composite membranes were thermally stable up to 140 °C, and exhibited remarkable toughness comparable to the parent polyDCPD. The three dimensionally continuous pore structure was confirmed by a combination of scanning electron microscopy (see image below), ionic conductivity and gas diffusion measurements. Potential applications of these novel membranes as high surface area catalyst supports, size selective membranes, and nanomaterial templates are currently being explored. This work was recently been published in the Journal of the American Chemical Society (volume 129, pages 13786–13787).



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