Block copolymer nanostructures

JUN-AUG 2008 | VOLUME 3 | NUMBER 3-4 38 Block copolymers occupy a huge area of research because they offer a vast range of possibilities for architecture, size, and chemical composition. Advances in polymer chemistry1, such as anionic polymerisation2 and most recently living radical polymerization3, have enabled a vast array of block copolymers to be synthesized with great control over their architecture, molecular weight, chemical composition, and functionality. Their intrinsic multi-properties allow the combination of different polymers and therefore the design of novel materials potentially comprising several different properties (e.g. thermoplastic, rubber, ductile, electrical conductivity, etc.). In bulk, when the different blocks are chemically immiscible, the balance between the entropically and enthalpically driven phase separation and the chemical bond constraints between the blocks drives the formation of ordered domains4–10. In solution, the interactions between the solvent and the different blocks dictate the ability to form well-defined structures. The architecture, molecular weight, volume fractions of blocks, and chemical functionality can all be set in the synthesis, making designer block copolymers a reality. The ability to effectively design nanoparticles and nanostructures to your preference, coupled with the wide range of applications associated with them, have made them an incredibly popular topic of research. Herein, One of the most important classes of synthetic systems for creating self-assembled nanostructures is amphiphilic block copolymers. By controlling the architecture of individual molecules, it is possible to generate nanostructures either in an undiluted melt or in solution. These ordered nanostructures are tunable over a broad variety of morphologies, ranging from discrete micelles and vesicles to continuous network structures. Their synthetic nature allows the design of interfaces with different chemical functional groups and geometrical properties. This, in combination with molecular architecture, determines the levels of ordering in self-organizing polymeric materials. For these and other reasons, block copolymer micelles, vesicles, and mesophases are finding applications in several areas, ranging from nanocomposites to biomedical devices.