Transition Metal Mediated Living Radical Polymerisation

Abstract

Living radical polymerisation has witnessed an unprecedented interest from polymer and materials scientists. Traditionally, polymers tended to replace natural materials such as wood, cotton and glass, and were used primarily for their structural features and performance and cost advantages. New functional polymers are essential for the manufacture of cell phones, lap-top computers, new cosmetics, and many pharmaceuticals. It is important to be able to control how monomers are put together within the macromolecule for the design at the molecular level for specific applications. Living polymerisation allows for end group control, polymer chain length and relatively narrow polydispersity polymers. In nature, the ability to control monomer distribution and chain length is obvious with approximately 20 amino acids being the monomers for polymers as diverse as hair, insulin and haemoglobin. Living radical polymerisation solves many of the problems in the use of monomers that contain heteroatoms and functional groups. These tend to be reactive towards strong nucleophiles and electrophiles which are required in ionic polymerisation. Protecting group chemistry as used in small molecule organic synthesis is not practical in polymer synthesis. Thus radicals that are inert to most functional groups and in particular protic species seem to be the answer. The mechanism of the transition metal mediate systems is extremely complicated with a range of organometallic species present in the reaction mixture. Solvents and coordinating monomers drastically affect the ideal reaction conditions and it is impossible to predict the optimum conditions for each synthesis without certain experiments being carried out. Nevertheless, catalyst systems are available which are acceptable and work well enough to be able to make a plethora of different macromolecules for a diverse range of applications /properties.