From Solid Block Copolymer To Highly Porous Membrane

A block copolymer, when stripped of one of its components, becomes a nanoporous material that is promising for use as a thin membrane separator in lithium-ion batteries, according to Marc A. Hillmyer and colleagues at the University of Minnesota, Minneapolis (J. Am. Chem. Soc., DOI: 10.1021/ja100985d). Membrane separators permit ions to migrate freely without allowing closely spaced anode and cathode components to contact each other. Separator technology also holds promise for numerous filtration and other energy-storage-related technologies. Hillmyer, Louis M. Pitet, and Mark A. Amendt started with triblock co­poly­mers composed of a linear polyethylene unit sandwiched between two polylactide units. Polylactide has gained popularity as a renewable, biodegradable polymer derived from plant sugars. The researchers exposed the molded co­poly­mer to sodium hydroxide, which etched out the polylactide segments. The result was a material with high porosity and controllable pore size—characteristics essential for effective battery separators. This method should be general for creating “nanoporous membranes of various sizes and thicknesses with the level of porosity dictated by the block polymer composition,” the researchers write.