Unusual Gas-Transport Selectivity in a Partially Oxidized Form of the Conductive Polymer Polypyrrole

Prior investigations have shown that polypyrrole has low gas-transport selectivity. This has been attributed to the microporous morphology obtained when thin films of this polymer are prepared by conventional synthetic methods. In this paper we show that polypyrrole with a dense (as opposed to microporous) morphology can be prepared by slowing down the rate of the polymerization reaction. We further demonstrate that a partially oxidized form of this material shows extraordinary gas-transport properties. When the volume percent of O 2 in the feed-gas stream was 100% (i.e., pure O 2 ), this partially oxidized form of polypyrrole showed an O 2 vs N 2 gas-transport selectivity coefficient of 18. This is one of the highest gas-transport selectivity coefficients to be reported to date for a polymeric material. The O 2 vs N 2 selectivity coefficient was found to increase with decreasing partial pressure of O 2 in the feed-gas stream. When the partial pressure of O 2 was 0.1% (99.9% N 2 ), the O 2 vs N 2 selectivity coefficient increased to 92. There is no precedent in the literature for selectivity coefficients of this magnitude for polymeric materials. The data are consistent with facilitated transport of O 2 in this unique partially oxidized form of polypyrrole.