what-is-raft cmse pdf standard
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RAFT – a process for making better polymersThe fundamental polymer chemistry in this presentation is referred from:
Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58, 379-410
CSIRO MATERIALS SCIENCE AND ENGINEERING
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What is RAFT?
RAFT (Reversible Addition-Fragmentation chain Transfer) technology is a very
sophisticated form of controlled free radical polymerization.
Often referred to as living polymerization, because it can be stopped and
restarted at anytime, this pioneering technology enables the synthesis of tailored
polymers with unprecedented control over composition and architecture.
MonomerRAFT Agent
Initiator
Polymer
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The RAFT agent
The key to the RAFT polymerization process is the RAFT agent; a small organic
molecule that is responsible for controlling growth
Z-group controls the
reactivity of the C-S doublebond; influences the rate of
radical addition and
fragmentation
Reactive C-S double bond
Free radical leaving group R•
(must be able to reinitiate
polymerization)
Weak C-S bond
R S Z
S
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Types of RAFT agents
Uses are dependent upon the RAFT agent selected:
Dithiobenzoates
• very high transfer constants
• prone to hydrolysis
• may cause retardation when used in high concentrations
Trithiocarbonates
• are readily synthesized
• high transfer constants
• cause less retardation and are more hydrolytically stable (than dithiobenzoates)
Xanthates
• lower transfer constants
• more effective with less activated monomers
• made more active by electron-withdrawing substituents
Dithiocarbamates
• activity determined by substituents on N
• effective with electron-rich monomers
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The RAFT polymerization process
Retained RAFT group (Y)
allows for furtherchemical manipulation
of the Polymer –
Macro-RAFT Agent
Polymer
R S Z
S
MonomerInitiator
R S Z
S
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The RAFT polymerization process
Living polymer chains: Active end-groups
Predetermined MW: Pn ~
[ RAFT Agent ]
[ Monomer]
Narrow MW distribution: Mw/Mn = 1.05 – 1.2
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Mechanism of RAFT polymerization
PnI
monomer (M)
initiation
X X
Z
R X X
Z
RPn X X
Z
Pn RPn
M
X X
Z
Pn X X
Z
PnPm X X
Z
Pm PnPm
M M
PmR
monomer (M)
c ain trans er
chain equilibration
reinitiation
k add
k -add
k
+
+
Pn Pm
termination
dead polymer+
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The RAFT process
Making polymers using the RAFT technology is as simple as 1, 2, 3.
Suitable
RAFT agent
Conventional plant, equipment
Controlledfree radical
polymerization
Simple to isolate, purify
well-definedpolymer
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How is RAFT different?
RAFT technology offers the polymer chemist the benefit of being able to more
readily synthesise polymers:
with a predetermined molecular weight over a wide range of monomers and
reaction conditions
with reactive terminal groups that can be purposely manipulated, including
further polymerisation
that is based on scalable manufacturing processes utilizing conventional
processing equipment
RAFT technology also provides the ability to design polymers with highly
complex architecture.
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Summary
Powerful tool for controlled free radical polymerization
“living polymerization” can be stopped and restarted
ability to design-in features systematically
Synthesis of specifically tailored polymers
unprecedented control over size, composition and architecture
desired physical and chemical properties
narrow molecular weight distribution
end-group removal
Growth of well defined polymers from any “surface”
small molecules, proteins, etc
Exploration of structure-function relationships of polymer conjugates rapid optimisation via high-throughput synthesis techniques
X
X X
X
XX
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