The synthesis of a benzo-15-crown-5 functionalized α-olefin (4′-(undec-10-enylcarboxylate)benzo-15-crown-5, 5) and its terpolymerization with carbon monoxide and various α-olefins are described. A decline of the glass transition temperatures (Tg) of the corresponding terpolymers was observed upon incorporating compound 5 into the polymer main chain. Ion-selective membranes were prepared by encapsulating the benzo-15-crown-5 functionalized α-olefin/CO terpolymers in a microporous polyethylene support. Preliminary ion-transport experiments demonstrate the ability of these novel crown ether substituted polyketones to transport NaClO4 across the membranes. Adjusting the polarity of the polyketones via the length of the olefinic side chain offers a means to control the ion-permeation-rates.