Double electron-electron resonance (DEER) spectroscopy is introduced as a new tool for the characterization of mesoscopic structures in polymers. This method can characterize distance distributions between spin probes in a range between 1.5 and 8 nm and can be applied to the measurement of ion cluster sizes and intercluster distances in ionically end-capped polymers by using ionic spin probes that attach themselves to the surface of the ion clusters. The results on intercluster distances for systems based on homopolymers are in agreement with earlier results from small-angle X-ray scattering (SAXS), while the cluster sizes can be rationalized by comparison with a force field molecular model of an ion cluster. The DEER experiment could also be applied to an ionically end-capped diblock copolymer for which a SAXS measurement of the intercluster distance failed.

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The size of ion clusters, distances between them, and the dynamics of their environment in ionically functionalized diblock copolymers were characterized by variable temperature continuous-wave electron paramagnetic resonance (CW EPR) and pulse double electron-electron resonance (DEER). CW EPR on ionic spin probes attached to the clusters reveals whether they are situated in the block copolymer interface and provides semiquantitative information on the fraction of cluster surface exposed to the polystyrene or polyisoprene microphase. DEER measurements show that ion cluster sizes do not depend on the topology of the ionomer and on chain length. For R,ω-macrozwitterionic block copolymers, where the clusters exhibit a two-dimensional distribution in the block copolymer interface, intercluster distances also do not depend on chain length. For monoionic species the intercluster distance obeys a 1 /3 scaling law with respect to the molecular mass of the polymer, suggesting constant polymer density and an unchanging spatial arrangement of the clusters.

The surface tension between the hydrophobic core and the solvent is known to play a major role in the self-assembly of diblock copolymer micelles in solution. Coulombic forces are also very important in the case of aggregates with weakly charged coronas. The aggregation number and morphology are often tuned by the addition of electrolytes to the solution via electrostatic screening and an eventual change in solvent quality. However, when the surface tension is low enough, dielectric discontinuity between the core and the solvent becomes important enough in comparison to other mechanisms, driving the surface tension at the same time it screens electrostatic interactions in the corona. Below, we demonstrate the importance of this effect for micelles with neutral and weakly charged coronas.