SELF-DIFFUSION COEFFICIENTS OF HYDROPHOBIC ETHOXYLATED URETHANE ASSOCIATING POLYMERS USING PULSED-GRADIENT SPIN-ECHO NUCLEAR-MAGNETIC-RESONANCE

The self-diffusion coefficients of hydrophobic ethoxylated urethane as sociating polymers of different molecular weights, but constant length of the hydrophobic end cap, were measured in aqueous solution using a pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) tec hnique. With increasing concentration, all polymers registered a decre ase in their mean diffusion coefficient accompanied by an increase in the dispersion of the diffusion coefficient about the mean. Both effec ts correlated with the pronounced concentration-dependent viscosity in crease characteristic of such polymers. The presence of hydrophobic en d caps decreased the diffusion coefficient by more than an order of ma gnitude relative to control polymers of identical size but lacking hyd rophobic modifications. The results are consistent with the prediction s of the transient micelle network model of network formation by such polymers and yield an estimate of the size (20 nm radius) and aggregat ion number (1 micelle contains 20 hydrophobic chains) for the associat ed clusters.