Highly conducting and strongly adhering polypyrrole coating layers deposited on glass substrates by a chemical process

To improve adhesion between polypyrrole and glass, new pyrrole-substituted organotrialkoxysilanes coupling agents are synthesized and studied. Solubility, hydrolysis, and self-condensation features in aqueous solutions are investigated by IR, (1)H, and (29)Si NMR spectroscopies. Varying the experimental conditions of pyrrole chemical polymerization on glass fibers surfaces indicates that a preliminary substrate treatment with these coupling agents and the use of a chemical vapor deposition process jointly lead to very thin (around 50 nm) polypyrrole layers with a particularly even and homogeneous aspect and adhering perfectly to glass surfaces. This last point has been plainly demonstrated by pull-out tests on conductive fibers embedded in resin and by tensile pull-off tests on silica plates. An unexpected effect of the use of specific silanes, when compared to commercial coupling agents, is an enhancement of polypyrrole conductivity (typically 150-200 S/cm), which can be related to the high regularity of the deposit.