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

Abstract

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 O2 in the feed-gas stream was 100% (i.e., pure O2), this partially oxidized form of polypyrrole showed an O2 vs N2 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 O2 vs N2 selectivity coefficient was found to increase with decreasing partial pressure of O2 in the feed-gas stream. When the partial pressure of O2 was 0.1% (99.9% N2), the O2 vs N2 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 O2 in this unique partially oxidized form of polypyrrole.