Micelle Formation and Inversion Kinetics of a Schizophrenic Diblock Copolymer

Abstract

It is known that the zwitterionic diblock copolymer, poly(4-vinylbenzoic acid)-b-poly(N-(morpholino)ethyl methacrylate) (VBA-b-MEMA), exhibits interesting “schizophrenic” micellization behavior (see: Liu, S.; Armes, S. P. Langmuir 2003, 19, 4432−4438). The kinetics of the pH-induced formation and dissociation of VBA−core micelles, the salt-induced formation and dilution-induced dissociation of MEMA−core micelles at pH 10, and the pH-induced micellar inversion between VBA− and MEMA−core micelles in the presence of 0.8 M Na2SO4 were studied in detail using stopped-flow apparatus equipped with a light scattering detector. A pH jump from 12 to 2 in the absence of salt leads to the formation of VBA−core micelles; upon a pH jump from 2 to 12, the breakup of VBA−core micelles into unimers occurs within the dead time of the stopped-flow apparatus (∼ 2−3 ms). At pH 10, addition of Na2SO4 (> 0.6 M) induces the formation of MEMA−core micelles. Compared to the pH-induced formation and dissociation of VBA−core micell...