Self-Diffusion Coefficients of Associating Polymers from Pulsed-Gradient Spin-Echo Nuclear Magnetic Resonance Spectroscopy

摘要

The self-diffusion coefficients ofhydrophobic ethoxylated ure-thane associating polymers of different molecular weights but a constant length of the hydrophobic end cap were measured in aqueous solution by a pulsed-gradient spin-echo NMR tech-nique. With increasing concentration, all polymers registered a decrease in their mean diffusion coefficient accompanied by an increase in the dispersion of the diffusion coefficient about the mean. Both effects correlated with the pronounced concen-tration-dependent viscosity increase characteristic of such polymers. The presence ofhydrophobic end caps decreased the diffusion coefficient by more than an order of magnitude rela-tive to that of control polymers of identical size but lacking such modifications, The results are consistent with the predic-tions of the transient micellar network model of network for-mation by such polymers and yield an estimate of the size (20-nm radius) and aggregation number (one micelle contains 20 hydrophobic chains) for the associated clusters.