Probing the gelation of polyvinylalcohol-water glutaraldehyde within a porous material by 1H n.m.r. — a preliminary investigation

Proton n.m.r. relaxation times ( T 1, T 2), chemical shift and line width of the solvent water protons in a polyvinylalcohol (PVA)-glutaraldehyde-water solution confined in a porous material (glass beads) revealed no significant changes during crosslinking and gel formation. Also, the self-diffusion coefficient was constant and identical to the self-diffusion coefficient of bulk water (2 × 10 −5 cm 2 s −1) during the reaction. Due to the smaller self-diffusion coefficient of the polymer molecules the solvent water resonance peak could be completely removed from the spectrum by applying a pulse gradient spin-echo technique, leaving only the signal from the polymer amenable for detection. In spite of the broadening effect caused by susceptibility differences between the solid porous matrix and the confined fluid, the PVA peaks were easily resolved. The observed distribution of self-diffusion coefficients of PVA could be approximated by three single diffusion coefficients ranging from 10 −6 to 10 −9 cm 2 s −1 at 25°C. The slower diffusion coefficient was found to decrease by almost an order of magnitude during the reaction with a rate of change of approximately 3 × 10 −5 s −1 at 80°C.