Dynamic Chain Exchange of Amphiphilic Alternating/Random Copolymer Micelles Promoted by Structural Uniformity and Flexibility

ABSTRACT Amphiphilic alternating and random copolymers bearing hydrophilic and hydrophobic side chains intramolecularly fold or intermolecularly assemble into size‐controlled unimer or multichain micelles in water. The random copolymer micelles are known to dynamically induce the exchange of the polymer chains, whereas effects of the main chain structures and composition/sequence distribution on the chain exchange behavior have been unexplored yet. Herein, we report the chain exchange behavior of the multichain micelles of amphiphilic alternating copolymers bearing hydrophilic poly(ethylene glycol) chains and hydrophobic dodecyl groups in water, compared with that of corresponding random copolymer micelles. From the kinetic analyses using fluorescence energy transfer, we reveal that the rate constant increases with increasing aggregation number of micelles, solution temperature, and polymer concentration. The chain exchange between the micelles undergoes via a unimer release/insertion and a micelle collision; the contribution of a micelle collision pathway increases with increasing polymer concentration and temperature. Importantly, the alternating copolymers with flexible and uniform molecular structures not only form monodisperse multichain micelles with narrow size distribution but also induce chain exchange between them faster than corresponding random copolymers containing composition/sequence distribution.