Rotational Dynamics of Spin-Labeled Polyacid Chain Segments in Polyelectrolyte Complexes Studied by CW EPR Spectroscopy

A nitroxide spin label has been covalently linked to the weak polyacid poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the rotational mobility of the polyacid backbone in polyelectrolyte complexes (PEC) formed with the oppositely charged strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) in dependence on the pH of the dispersion and the temperature. The rotational mobility of the polyacid chain segments has been determined by simulation of the line shape of the continuous wave (CW) electron paramagnetic resonance (EPR) spectra using the microscopic order/macroscopic disorder (MOMD) model of restricted rotational diffusion. The study has shown that the diffusion coefficient characterizing the rotational motions of the polyacid backbone is significantly smaller at low degree of dissociation at pH 4 than at high degree of dissociation at pH 7 and pH 10.