Statistical, Gradient, Block and Graft Copolymers by Controlled/Living Radical Polymerizations: 159 (Advances in Polymer Science) - Tapa dura

The design and the realisation of well defined polymer architectures has become an important goal in macromolecular science. The prerequisite for achieving this goal is the availability of controlled polymerisation reactions. Living anionic polymerisation was the first reaction fulfilling these requirements. Cationic polymerisation only came into play when it was realised that it was possible to create an equilibrium between active and dormant species with the fraction of the dormant species being far superior to that of active ones. A corresponding principle applies to controlled radical polymerisation per formed in quite a number of modes such as nitroxide mediated polymerisation (NMP), atom transfer radical polymerisation (ATRP), reversible addition frag mentation chain transfer (RAFT) or catalytic chain transfer (CCT) reactions. All of these variants of controlled radical polymerisation lead to well defined archi tectures with the particular advantage that a much larger number of monomers are suitable and the reaction conditions are much less demanding than those of living ionic polymerisation reactions. Although in controlled radical polymerisation, termination reactions cannot be excluded completely, they are limited in their extent and consequently the mol ecular weight is controlled, the polydispersity index is small and functionalities can be attached to the macromolecules. These features are indicative of the real isation of well defined polymer architectures such as block copolymers, star shaped and comb shaped copolymers.

This review is focused on controlled/living radical polymerization methods for the preparation of various copolymers. A brief introduction to the subject of radical polymerization, and early attempts to control it, is followed by a detailed examination of the literautre on controlled/living radical copolymerizations from the mid-90's until 2001. The topics covered include statistical/gradient, block, graft, and star copolymers and the polymerization methods used to produce them. These copolymers were prepared using three major controlled radical methods (either nitroxide mediated polymerization, atom transfer radical polymerization or degenerative transfer) and a combination of polymerization techniques, including transformation chemistry or the simultaneous/dual living polymerizations, to achieve the desired chain architecture or topology. An evaluation of the current state of the field is also presented.