Odd–Even Effect on Rotational Dynamics of Spin-Labeled Polyacid Chain Segments in Polyelectrolyte Multilayers

A nitroxide spin label has been covalently attached to the weak polyelectrolyte poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the rotational dynamics of the polyacid backbone in swollen polyelectrolyte multilayers (PEMs) formed by P(E-alt-MA) and the oppositely charged weak polycation poly(allylamine hydrochloide) (PAH) by continuous wave electron paramagnetic resonance (EPR) spectroscopy. The growth of the PEM film with increasing number of layers has been monitored by quantitative EPR using the spin-labeled polyanion (SL-P(E-alt-MA)) for the preparation of every polyanion layer. A parabolic growth has been found for PEMs with up to 16 layers. In further experiments the SL-P(E-alt-MA) has been placed in selected layers, and the line shape has been analyzed. A pronounced odd–even effect has been observed, i.e., the rotational dynamics of the P(E-alt-MA) backbone in the PEMs is influenced by the chemical nature of the polyelectrolyte in the terminating layer.