H-1-NMR SELF-DIFFUSION AND MULTIFIELD H-2 SPIN RELAXATION STUDY OF MODEL ASSOCIATIVE POLYMER AND SODIUM DODECYL-SULFATE AGGREGATION IN AQUEOUS-SOLUTION

H-1 NMR self-diffusion and multifield H-2 spin relaxation measurements were applied in a study of the aggregation of a model associative pol ymer (MAP) in aqueous solution. The polymer is based on a poly(oxyethy lene) backbone with ether-linked alkyl chains ends. The aggregation wa s studied also in presence of sodium dodecyl sulfate (SDS) at a high c oncentration. Associative polymers self-assemble in aqueous solution i nto what is generally believed to be micelle-like aggregates with the hydrophobic end groups situated in the micellar core. In binary soluti ons of polymer and water such polymer aggregates were found to display an extensive polydispersity which increased with polymer concentratio n, as based on experimental self-diffusion data. Corresponding measure ments on mixed solutions of high SDS concentration, on the other hand, indicate that SDS micelles act as seeds for aggregation, promoting a markedly lower polydispersity for these mixed aggregates. H-2 spin rel axation data on SDS molecules in mixed aggregates were found to be con sistent with a two-step motional model for chain reorientation. The fa st local anisotropic motions of the SDS molecules inside the aggregate s were found not to be particularly influenced by the addition of poly mer, whereas the slow isotropic motions of the SDS molecules, such as aggregate tumbling and lateral diffusion of SDS over the curved aggreg ate surface, were considerably retarded. The increased size of the mix ed aggregates upon addition of polymer is probably the main reason for this retardation of reorientational dynamics. However, the motion of the polymer in the mixed aggregates and in single-component polymer ag gregates could not be described by the same motional model; instead a three-step motional model had to be applied. The additional very slow motion component was interpreted to be a reptational or exchange motio n of the polymer inside or between aggregates.