Characterization of Ionic Clusters in Different Ionically Functionalized Diblock Copolymers by CW EPR and Four-Pulse Double Electron−Electron Resonance

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 α,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.