Fishing for KF : Potassium fluoride and chloride salts can be extracted from aqueous media using poly(methyl methacrylate)s containing pendant calix[4]pyrrole and crown ether groups (see picture). These polymers are able to extract these salts much more efficiently than calixpyrrole, crown ether, linked crown ether calixpyrrole monomers, polymers containing either recognition unit, or poly(methyl methacrylate) controls.