Redistribution of Block Copolymer Chains between Mixed Micelles in Solution

The evolution of polymolecular micelles formed by two different poly(2-vinylpyridine)-polystyrene (PVP-PS) block copolymers dissolved in toluene is studied by means of transmission electron microscopy (TEM). The two PVP-PS diblock copolymers differ in composition, namely in the length of PVP block. Upon dissolution, a rapid formation of mixed polymolecular micelles takes place. As a result, the micellar size distribution observed is rather broad already at this initial stage. Due to the presence of two different diblock copolymers, the process of micellar growth involves not only the fusion of micelles but also the chain exchange between polymolecular micelles of different composition, which may slow the equilibration process. After a considerable aging time, the block copolymers seem to reach the equilibrium state, and an almost perfect bimodal size distribution is observed. According to the theoretical analysis given, both "pure" and "mixed" micelles constitute the micellar size distribution.