Local Chain Dynamics in Polyelectrolyte Multilayers of Chitosan and Spin-Labeled Poly(ethylene-alt-maleic acid)

The cationic charged chitosan and the weak polyacid poly(ethylene-alt-maleic acid) are used to build polyelectrolyte multilayers (PEMs). To study the rotational dynamics of the polymer backbone in the swollen state of the PEMs using electron paramagnetic resonance spectroscopy, a nitroxide spin-label is covalently attached to the polyacid. It is found that spectra of PEMs with even number of layers show a superposition of two spectral components: a major, slow-motion component, which arises from chain segments intrinsically compensated by protonated amino groups of the chitosan, and a minor, fast-motion component, which is assumed to originate from loops and tails of the polyacid chain located at the surface of the PEMs. The dissociated acid groups in the loops and tails are extrinsically compensated by small counterions and the rotational mobility of these chain segments is consequently much higher compared to chain segments interacting with the oppositely charged chitosan.