From "sunflower-like" assemblies toward giant wormlike micelles

One of the most interesting and fascinating solution properties of block copolymers is their ability to self-assemble into micelles, lamellar aggregates, and vesicles. Such organized structures have made diblock copolymers of great importance in nanotechnology applications.(1-11) For instance, the spontaneously formed vesicles in water are potentially useful as vehicles for delivering drugs and as biomimetic models of biological cells. We show here for the first time that the cyclization of a linear copolymer chain induces a remarkable change in the micellar morphology. This result is highlighted in the case of linear and cyclic polystyrene - polyisoprene (PS - PI) diblock copolymers having exactly the same molar weight and dispersed in a selective solvent for PI. The micelles arising from linear diblock copolymers exhibit a monodisperse spherical shape (50 nm in diameter) whereas those formed from cyclic copolymers are long (> 1 mum) cylindrical (wormlike) objects resulting from the unidirectional self-assembly of "sunflower-like" elementary micelles whose architecture strongly favors the core-core (PS-PS) attractions. We expect these new cyclization-based design copolymer architectures morphologies will be of particular interest in future nanotechnology applications.