Fission of giant vesicles accompanied by hydrophobic chain growth through polymerization-induced self-assembly

In order to clarify the formation mechanisms of micrometer-sized spherical vesicles through the polymerization-induced self-assembly of amphiphilic poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid), PMAA-b-P(MMA-r-MAA), the nitroxide-mediated photocontrolled/living radical polymerization initiated by a PMAA end-capped with 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl was performed in an aqueous methanol solution. The polymerization proceeded in a living manner during the self-assembly. The vesicles produced during the early stage of the polymerization were not completely spherical and had dents and very small holes on their surface. As the hydrophobic P(MMA-r-MAA) block chains grew by the polymerization, the contorted vesicles were changed into half-sized elliptical vesicles accompanied by enlargement of the dents and holes. The vesicles were finally transformed into much smaller spherical vesicles by further growth of the hydrophobic chains. The mechanisms of the vesicles by fission involved the outside separation by the expansion of the dents and holes on the surface and the inside separation by budding.