Aggregation behavior of a symmetric, fluorinated, telechelic polymer system studied by 19F NMR relaxation

F-19 NMR experiments are used to study the aggregation behavior of two telechelic polymer systems. These polymer systems consist of a water-soluble chain, here poly(ethylene glycol), with two hydrophobic endgroups. Because of the hydrophobic interaction of the fluorocarbon endgroups, these polymer chains associate in water to form aggregates at low concentrations. The aggregate comprises a core formed from the insoluble hydrophobic endgroups that are surrounded by a corona of long water-soluble polymer chains. With increasing polymer concentration, the polymer chains start bridging so that a three-dimensional, physical network with fluorinated aggregate cores as cross-link points is formed. This effect can be substantially enhanced by replacing the hydrophobic endgroup C6F13 With C8F17, a consequence of the stronger association of C8F17 in aqueous solution. By different F-19 NMR parameters, i.e., F-19 transverse relaxation and F-19 chemical shift, we can distinguish aggregated and nonaggregated chain ends. This enables us to follow the formation of an infinite network.