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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.
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.
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