Size and solution behavior of sodium 10-undecenoate oligomers

Sodium 10-undecenoate oligomers were prepared by [gamma]-irradiation of aqueous solutions of the monomer at concentrations above and below the critical micelle concentration (cmc). Number-average molecular weights indicated degrees of polymerization of 6 and 8, respectively. Weight-average molecular weights were roughly 60% greater, showing both oligomers to be somewhat polydisperse. Measurements of viscosity, counterion activity, and conductance as a function of oligomer concentration suggested aggregation of the oligomers into larger structures as the concentration increased. This was supported by electron spin resonance measurements using spin-labeled probes and by fluorescence quenching studies. The ultimate size of the aggregating oligomers was found to correspond to that of ordinary micelles formed from sodium 10-undecenoate monomers. The behavior of the oligomers formed above the cmc closely paralleled that of the oligomers formed below the cmc. 26 refs., 10 figs., 2 tabs.