H-1 NMR self-diffusion study of PVA cryogels containing ethylene glycol and its oligomers

The multicomponent self-diffusion of the PVA cryogels prepared by a freezin g-thawing treatment of the water/oligooxyethylene glycol solutions of PVA h as been studied with the NMR FT-PGSE method at various temperatures and com pared with the diffusion of such systems without glycols. The evaluated app arent activation energies, E-a, of the self-diffusion for the PVA chains sh owed that entrapment of ethylene glycol, EG, and diethylene glycol, DEG, in to cryogels made them more friable. These glycols acted as cryoprotectants. On the contrary, triethylene glycol, TEG, and, especially, PEG-400 made cr yogels firmer. The E-a values for the self-diffusion of oligooxyethylene gl ycols exceeded those for the water molecules in the same cryogel and increa sed along with the lengths of oligomers. These values are also above those obtained for the PVA chains in cryogels with EG, DEG, and TEG as well as wi thout additives. This fact is in conformity with the mechanism of the phase separation of water and co-solvent by freezing the multicomponent system. It is expected that the presence of TEG and PEG-400 in cryogels leads to a decrease in dimensions of the solvent-filled pores and the PVA filaments li ke that which was found out earlier for DMSO containing cryogels. Such a co mpartmentation within cryogels depends mainly on the dimensions of ice and polymer microcrystallites formed by freezing the solution. (C) 1999 Academi c Press.