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Non-Centrosymmetric Cylindrical Micelles by Unidirectional Growth

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Science  03 Aug 2012:
Vol. 337, Issue 6094, pp. 559-562
DOI: 10.1126/science.1221206

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Unidirectional Growth

Block copolymers, in which two dissimilar polymers are covalently joined together, can be designed to form micelles in solution and can be used as self-assembling injectable gels for tissue engineering or wound healing. One challenge is to find ways to create asymmetrical structures, because normally, block addition would occur at both ends of the polymer chain. Rupar et al. (p. 559; see the Perspective by Pochan) devised a route to link together three diblock copolymers with a capping approach. Protecting one end during growth gave rise to asymmetrical structures.

Abstract

Although solution self-assembly of block copolymers (BCPs) represents one of the most promising approaches to the creation of nanoparticles from soft matter, the formation of non-centrosymmetric nanostructures with shape anisotropy remains a major challenge. Through a combination of crystallization-driven self-assembly of crystalline-coil BCPs in solution and selective micelle corona cross-linking, we have created short (about 130 nanometers), monodisperse cylindrical seed micelles that grow unidirectionally. These nanostructures grow to form long, non-centrosymmetric cylindrical A-B and A-B-C block co-micelles upon the addition of further BCPs. We also illustrate the formation of amphiphilic cylindrical A-B-C block co-micelles, which spontaneously self-assemble into hierarchical star-shaped supermicelle architectures with a diameter of about 3 micrometers. The method described enables the rational creation of non-centrosymmetric, high aspect ratio, colloidally stable core-shell nanoparticles in a manner that until now has been restricted to the biological domain.

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