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Tightening Polyelectrolyte Multilayers with Oligo Pendant Ions.

A series of polycations bearing one, two, and three pendant quaternary ammonium groups per repeat unit has been synthesized and combined with poly(sodium 4-styrenesulfonate) to produce hyperthin polyelectrolyte multilayers. Incremental addition of quaternary ammonium groups per repeat unit leads to decreased permeances for H2, CO2, and N2 and increased H2/CO2 and CO2/N2 permeation selectivities. These results, together with analysis of the composition from X-ray photoelectron spectra and values of Young's modulus from nanoindentation analysis, show that oligo pendant ions provide a means for increasing volume charge density and tightening polyelectrolyte multilayers.