Supramolecular Engineering with Macromolecules: An Alternative Concept for Block Copolymers
✍ Scribed by Bas G. G. Lohmeijer; Ulrich S. Schubert
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 133 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0044-8249
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✦ Synopsis
Block copolymers represent an important class of materials, which have received widespread attention because of their remarkable micro-and nanophase morphology. This morphology leads to unique properties compared to homopolymers or their blends. Classical examples of block-copolymer morphology are lamellae, hexagonal-packed cylinders and body-centered-cubic arrays of spheres. [1] During the last decades, important advances have been made in the synthesis, characterization, and application of block copolymers. In particular, anionic polymerization has been successfully applied in their controlled synthesis. [2] Several other routes have been realized as well, for example, controlled radical polymerization, [3] cationic polymerization, [4] group transfer, [5] and metathesis, [6] or combinations of such techniques. Nevertheless, block-copolymer synthesis remains a challenge for certain materials and several interesting combinations could not be realized to date. On the other hand, recent developments in the field of supramolecular chemistry have shown that small (self-)complementary building blocks can lead, through self-organization processes, to large, well-defined structures, which are held together by noncovalent interactions such as hydrogen bonds [7] and metal-to-ligand coordination. [8] Herein we present a new highly controlled and welldefined construction principle for block copolymers that utilize supramolecular interactions, in this case metal-toligand coordination. By this method new combinations of block copolymers can be prepared, which are not accessible, or have been very difficult to access to date. This allows a comparison of the new metallo-supramolecular compounds with classical well-documented covalent block copolymers. For this purpose we chose the terpyridine ligand as the central building unit, which is well-known for its outstanding ability to form stable bis complexes with a large variety of transitionmetal ions (Figure 1). [9] The main advantage of having a metal complex as the bridging unit is the possibility of cleavage at this junction point. Therefore new ™smart materials∫ are accessible. Moreover, the metal ion being at the interface between the blocks may cause additional interesting features regarding morphology, thermal and mechanical as well as photophysical properties.
The construction of the supramolecular block copolymers works along the same principle as their covalent counterparts.