what-is-raft cmse pdf standard

8/12/2019 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



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

www.csiro.au/products/RAFT |

http://www.csiro.au/products/RAFT




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






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






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






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






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+








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






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.






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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