Mechanism of Molecular Exchange in Diblock Copolymer Micelles: Hypersensitivity to Core Chain Length

Molecular exchange between spherical micelles formed from isotopically labeled diblock copolymers was investigated using time-resolved small-angle neutron scattering measurements. Temperature changes affect the micelle exchange rate R(t) consistent with melt dynamics for the core polymer. Varying the core block length N produces gigantic changes in R(t) due to the thermodynamic penalty associated with ejecting a core block into the surrounding solvent. This hypersensitivity, combined with modest polydispersity in N, leads to an approximately logarithmic R(t).