Unexpected toroidal micelles formed from St/MMA gradient copolymers

Toroidal micelles are of great interest and rarely observed in gradient copolymer systems. Herein, we report massive toroidal micelles formed from styrene (St)/methyl methacrylate (MMA) gradient copolymers using a common solvent mixing method followed by a cooling-heating procedure. Furthermore, we demonstrate that the obtained toroidal morphology is sensitively dependent on a heat treatment procedure. Solely spherical micelles are obtained by a common solvent mixing method. These spherical micelles could be transformed into toroidal micelles via vesicles during a cooling-heating process. When a reverse heating-cooling process is adopted, no toroidal micelles formed. Thus, these results add new members to the family of toroidal micelles and reveal pathway dominating morphologies in gradient copolymer micelles.

Automated summary

In this study, massive toroidal micelles were formed from styrene/methyl methacrylate gradient copolymers using a common solvent mixing method followed by a cooling-heating procedure. It was found that the obtained toroidal morphology was sensitively dependent on the heat treatment procedure. Spherical micelles could be transformed into toroidal micelles via a cooling-heating process, whereas no toroidal micelles were formed when a reverse heating-cooling process was adopted. These results contribute to the understanding of toroidal micelles and their formation pathways in gradient copolymer systems.