Graphene as a target for polymer synthesis

Abstract

Graphene has remarkable physical properties, but existing production methods have severe deficiencies that limit its potential use in robust technologies. Opening a reliable and efficient synthetic route to graphene and its functionalized derivatives offers a path to overcome this obstacle for its practical application. Graphene can be regarded as a two-dimensional polymer (2D), and it is here argued that it, along with its derivatives, represents a realistic yet challenging target for polymer synthesis. In order to demonstrate the possibility of such syntheses, an overview is presented on the evolution of phenylene-based macromolecules. It is shown how classical linear polyphenylenes can be expanded to increasingly more sophisticated structures involving two- and three-dimensional (3D) polyphenylene architectures. A crucial aspect of the meticulous synthetic design of these molecules has been the avoidance of defects within the structures, resulting in the precise control of their physical, especially optoelectronic, properties. Linear conjugated polymers with defined optical properties have been made by controlling the degree of torsion between the benzene rings. This has included the development of efficient routes to ladder-type polymers and of step-ladder materials. Planar graphene molecules, or nanographenes, in a range of sizes and shapes have been fabricated by the controlled cyclodehydrogenation of 3D polyphenylene dendrimers. By combining knowledge gained from the synthesis of conjugated polymers, polyphenylene dendrimers, and nanographenes, it has proven feasible to make, either by solution or surface-bound methods, graphene nanoribbons with well-defined structures. These functional materials possess properties similar to graphene while displaying improved processability. Finally, we review less-sophisticated paths towards graphene materials involving processing of graphene oxide, its reduction, and its hybridization with other components. These too have a role to play in acquiring functional graphenes where a lesser degree of control over the properties is required. This voyage of exploration towards the precise synthesis of conjugated phenylene-based polymers has thus had the dual objectives of fundamental research and practical materials science. En route we have had to meet the sometimes conflicting gauntlets thrown down by these two aims, which has at times involved trade-offs between the theoretically desirable and the reasonably accessible. © Springer-Verlag Berlin Heidelberg 2013.