Worm-like vesicle formation by photo-controlled/living radical polymerization-induced self-assembly of amphiphilic poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid)

The formation mechanisms of worm-like vesicles were determined by the photopolymerization-induced self-assembly of an amphiphilic poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid) diblock copolymer, PMAA-b-P(MMA-r-MAA). The photopolymerization-induced self-assembly was performed by the nitroxde-mediated photo-controlled/living radical polymerization in an aqueous methanol solution using a PMAA end-capped with 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl. The polymerization retained its living nature during the self-assembly. The copolymer during the early stage of the polymerization produced cup-like vesicles that had some holes in the surface and were comprised of a thin and flexible bilayer. As the hydrophobic P(MMA-r-MAA) block chain was extended by the polymerization progress, the cup-like vesicles were transformed into spherical vesicles, accompanied by decreases in the number of holes and their size. Further extension of the hydrophobic block chain enhanced the intervesicular aggregation to provide worm-like vesicles. These morphological changes were accounted for by variation in the critical packing shape of the copolymer by expansion of the hydrophobic chain volume.