Reversible Addition Fragmentation Chain
Transfer (RAFT) Polymerization
Free radical polymerization has been
revolutionized over the last years by the invention and development of
techniques that allow to control the polymerization process with respect to
the polydispersity of the molecular weight distribution and the formation of
complex macromolecular architectures, such as
block-copolymers,
comb-copolymers,
starpolymers,
gradient copolymers etc.
Especially the RAFT process has proven to be one of the most powerful and
versatile of the new living free radical polymerization techniques. The
controlling agents used in most RAFT polymerizations – the dithioesters –
have been developed in great structural variety and can be used to mediate
the polymerizations of many monomers, i.e. from styrene, acrylates and
methacrylates to vinyl acetate and various functionalized monomers. Ionic
polymerization methods for the synthesis of advanced macromolecular
architectures are generally less versatile, for their application is limited
to certain monomers and they require demanding experimental conditions. It is the
unique versatility of the RAFT process and its ability to generate the above
mentioned architectures that makes it a highly attractive method to generate
new materials with unsurpassed properties that otherwise would not be
obtainable. Applications range from polymeric drugs over nanoparticles and
biocidal polymers to self organizing membranes.
At the Institute of Physical Chemistry of the University of Goettingen we
use our expertise in living free radical polymerization to perform research
in both the basic mechanistic and kinetic fundamentals and industrial
applications of the ‘Reversible Addition Fragmentation Chain Transfer
(RAFT)’ polymerization. Our present work mainly focuses on the controlled
radical polymerization of vinylic monomers with major industrial
significance under specific reaction conditions: Polymerization under high
pressure (100 > p > 3000 bar) are performed to gain knowledge about the
characteristics of the individual reaction steps that govern the RAFT
process and in order to increase control in the polymerization of highly
substituted monomers. Detailed studies of RAFT polymerizations in
supercritical solutions open up completely new solvent environments for living radical
polymerizations. Additional work is directed to the immobilization of the
mediating agents to effectively remove them from the final polymeric
material.
Although the exact mechanism of the RAFT process is still subject of ongoing
scientific discussion, new and more effective RAFT agents are constantly
emerging. RAFT polymerizations are not only performed in classical homo and
solution polymerizations, but are also capable of controlling radical
polymerizations in aqueous media and on surfaces.
From macromolecules with complex topology - such as star polymers that can
be obtained via RAFT polymerization in a very uniform fashion - novel
molecular nano-carriers are developed, which are designed for transportation
of biomedical agents or for immobilization of dyes in polymeric materials.
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Research
project descriptions◄
last edited:
Sept. 02, 2008
