The synthesis of 3-octadecyl- and 3-docosylpyrrole, their polymerisation and incorporation into novel composite gas sensitive resistors

3-Octadecylpyrrole and the novel 3-docosylpyrrole were synthesised in high yields. These monomers were polymerised with various oxidising agents to produce a range of 3-octadecylpolypyrroles and 3-docosylpolypyrroles with different counter-ions. These polymers were soluble in chloroform and were readily coated onto microporous poly(vinylidene fluoride) membranes. 3-alkylpolypyrrole–tin(IV) oxide composites were also produced by adding finely ground tin(IV) oxide to a solution of the 3-alkylpolypyrrole in chloroform and drop-coating the resulting mixture onto alumina substrates or poly(vinylidene fluoride) membranes. The resulting 3-alkylpolypyrrole based materials were tested for their gas sensitivity towards a number of classes of volatile organic compounds (VOCs). The 3-alkylpolypyrrole–tin(IV) oxide composites were found to exhibit enhanced sensitivity and differing selectivities to VOCs when compared to tin(IV) oxide or the 3-alkylpolypyrrole alone. Previously, conducting polymers exhibited little response to non-polar VOCs, in contrast 3-octadecylpolypyrrole-nitrate–tin(IV) oxide composite sensors were particularly sensitive to hydrocarbons and could detect butane and propane at concentrations well below their lower limit of explosion (LLE).