Diffusion of molecular probes and the effects of their interactions with polymer matrices as studied by pulsed-field gradient NMR spectroscopy

Abstract

Pulsed-field gradient NMR spectroscopy was used to study the interactions between small molecular probes and polymers bearing interacting groups. The self-diffusion coefficients of ethylene glycol and its oligomers and their methyl ester derivatives in poly(vinyl alcohol) gels were measured to study the effect of hydrogen bonding. The self-diffusion coefficients of small molecular probes containing hydroxyl, amine, and carboxylic acid groups were determined in several polymer matrices including poly(vinyl alcohol), poly(allylamine), and poly(acrylic acid) bearing lateral hydroxyl, amine, and carboxylic acid groups, respectively. The ionic interactions between the functional groups of the diffusants and of the polymers exhibited a marked effect on the diffusion of the molecular probes. For example, the reduced self-diffusion coefficients measured for a diffusant with a carboxylic acid group in a poly(allylamine) matrix were shown to be lower even though the molecular masses of the diffusants are similar.Key words: pulsed-field gradient NMR spectroscopy, self-diffusion, intermolecular interactions.