THE ASSOCIATION OF URETHANE-POLYETHYLENEOXIDE (HEUR) THICKENERS, AS STUDIED BY NMR SELF-DIFFUSION MEASUREMENTS

The concentration and molecular weight dependence of the self-diffusion coefficient (D(self)) of associative polymers of HEUR-type in aqueous solution have been investigated using FT-PGSE-NMR technique. The idea of three-dimensional network formation as a result of aggregation of the hydrophobic end-groups of the polymer in junctions is supported through the observed dramatic lowering of D(self) with increased concentration. The network-formation efficiency depends on the polymer molecular weight as well as the hydrophobicity of the end-groups. A double logarithmic dependence of the self-diffusion coefficient versus concentration (c) has been observed: D(self) infinity c(-a1,a2). The first exponent, a1, is valid at low concentration, < 1% polymer per weight solution, and ranges from 0.5 to 1, whereas the second exponent, a2, describing systems of higher concentration, ranges from 2 to 2.7.