Electrochemical, Pulse-Field-Gradient Spin-Echo NMR Spectroscopy, and ESR Spectroscopic Study of the Diffusivity of Molecular Probes inside Gel-type Cross-linked Polymers

The permeability of five geltype synthetic resins, obtained by polymerization of 1-vinylpyrrolidin-2-one cross-linked with N,N’-methylenebis- ACHTUNGTRENUNGacrylamide (1, 2, 3, 4, and 5 wt%) and swollen by N,N-dimethylformamide (DMF), has been analyzed. The diffusion of 2,2,6,6-tetramethyl-4-oxo-1-piperidinyloxyl (TEMPONE) was studied by ultramicroelectrode voltammetry. Similar measurements were performed for solutions of non-crosslinked poly(vinylpyrrolidone) in DMF. To provide information on the rotational mobility of TEMPONE and the translational mobility of DMF, electron spin resonance (ESR) spectroscopic and pulsed-field-gradient spin-echo nuclear magnetic resonance (PGSENMR) spectroscopic experiments, respectively, were carried out. Comparative analysis of the results obtained by electrochemical, ESR spectroscopic, and PGSE-NMR spectroscopic measurements showed that diffusivity inside the polymer framework is significantly affected by the extent of cross-linking, the size of the diffusing probe, and the presence of electrolytes.