Self-diffusion in poly( N? -vinyl pyrrolidone) - poly(ethylene glycol) systems

We have applied the PFG NMR technique to investigate the translational mobility in the PVP-PEG system as a function of composition and temperature at the stages of PVP-PEG complex formation, its swelling, and dissolution in excess of liquid PEG. It has been found that the variations of the spin-echo attenuation with PEG content, water amount, and temperature reflect the different stages. The first two stages are characterized by a distribution of the self-diffusion coefficients of PEG involved in the network. The dissolution shows two diffusion coefficients; the fast one is attributed to PEG molecules, the slow one to the associates of PEG and PVP. The temperature dependencies can be described by an Arrhenius law with an activation energy depending on the composition of the blend. The concentration dependence of the PEG self-diffusion coefficients in the blend occurred to be independent of the molecular weight of PVP. The results are discussed in terms of the Mackie-Meares model.[PUBLICATION ABSTRACT]