raft choosing the right agent

8/21/2019 RAFT Choosing the Right Agent

1/19

www.csiro.au/products/RAFT | Page 1

CSIRO MATERIALS SCIENCE AND ENGINEERING

RAFT choosing the right agentThe fundamental polymer chemistry in this presentation is referred from

Moad G, Rizzardo E, Thang SH. 2005.Aust. J. Chem. 58: 379-410.
http://www.csiro.au/products/RAFThttp://www.csiro.au/products/RAFT


2/19


Conventional free radical polymerisation

ADVANTAGES:

Simple to implement

Tolerant of a wide range of monomers and

reaction conditions

Inexpensive

LIMITATIONS:

Relatively broad molecular weight distribution

Copolymers heterogeneous in composition

Little scope for making blocks or more complex

architectures

20,000 monomers 500 monomers


3/19


RAFT polymerisation technology

Living polymer chains:

Predetermined MW:

Narrow MWdistribution: Mw/Mn= 1.05 1.2

[ RAFT Agent ]

Pn[ Monomer]

~

Active end-groups


4/19


RAFT polymerisation technologyThe RAFT agent (X-Y)

Z-group controls the

reactivity of the C-S double

bond; influences the rate of

radical addition and

fragmentation

Reactive C-S double bond

Free radical

leaving group R

must be able to reinitiate

polymerisation

Weak C-S bond

R S Z

S


5/19


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


6/19


RAFT polymerisation technology

Retained RAFT group (Y)

allows for furtherchemical manipulation

of the polymer

macro-RAFT agent

Polymer

R S Z

S

MonomerInitiator

R S Z

S


7/19


Mechanism of RAFT polymerisation

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)

chain transfer

chain equilibration

reinitiation

kadd

k-add

k

+

+

PnI

monomer (M)

initiation

Pn Pm

termination

dead polymer+


8/19


How to select RAFT agents

Ph MeS H3C N F

F F

O N

O

PhO EtO N

H3C

Ph

N

Et

Et

methylmethacrylate vinylacetate

N-vinylpyrrolidinone

styrene,methylacrylate,acrylamide,acrylonitrile

CH3NC

CH3

CH3Ph

CH3

H

NC

Ph

CH3EtO2C

CH3

CH3

CH3

H3C

H3C

H3C

H

H

H

NC

CH3

H

Ph

CH3

H3C

H3C

H3C

H

Ph

H

H

NC

H

methylmethacrylate

styrene,methylacrylate,acrylamide,acrylonitrile

vinylacetate,N-vinylpyrrolidinone

Zgroup: addition rates decrease and fragmentation rates increase from left to right

Rgroup: fragmentation rates decrease from left to right

R S Z

S


9/19


CTA structure Styrenes Acrylates Acrylamides Methacrylates Methacrylamides Vinyl Esters Vinyl Amides

o o

o o

o o

o o

o o o o

o o o o

RAFT agent monomer matching

oNo control of molecular weight dispersity or severe retardation/inhibition

Limited control of molecular weight dispersity (


10/19


CTA structure Styrenes Acrylates Acrylamides Methacrylates Methacrylamides Vinyl Esters Vinyl Amides

o o o o

o o

o o o

o o

o o

RAFT agent monomer matching (cont.)

oNo control of molecular weight dispersity or severe retardation/inhibition

Limited control of molecular weight dispersity (


11/19


RAFT agents core set

Vinyl acetate

N-vinylpyrrolidinoneN-vinyl carbazole

Styrene

Methyl acrylateAcrylamide

Acrylonitrile

Methyl methacrylate

MethacrylamidesStyrene

Methyl acrylate

Acrylamide

Acrylonitrile


12/19


End-functional PMMA synthesis

24 28 32 36 40

elution volume (min)

Moad G, Chong YK, Rizzardo E, Postma A, Thang SH. 2005. Polymer. 46: 8458-8468.

Over ~50-fold range of RAFT agent concentrations

Little retardation

Low dispersities/monomodal distributions

[RAFT] x102M Mn Mw/Mn % Conv.

19.92 2600 1.17 80

9.96 4600 1.15 80

4.95 9300 1.11 79

2.48 20600 1.09 91

1.24 39600 1.09 >99

0.61 8400 1.11 >99

0.32 12500 1.16 >99

MMA + Vazo-88 + HOOCCH2CH2 SCS-R HOOC PMMASCS-R90C

6 hrs

S S

CN


13/19


A-B diblock copolymers

Poly(BA-b-AA)

Mn= 52,400

Mw/Mn= 1.19

Poly(BA)

Mn= 33,600

Mw/Mn= 1.13


14/19


Time (hr) Mn Mw/Mn % Conv.

8 55,400 1.05 31

16 86,200 1.04 50

40 135,900 1.05 83

Star polymers 6-arm star polystyrene

Mayadunne RTA, Moad G, Rizzardo E. 2002. Tetrahedron Letters. 43: 6811-6814.


15/19


Luminescent block copolymers

Chen et al. 2008. Chem Comm. 1112.


16/19


End-group removal/transformation

Chong YK, Moad G, Rizzardo E, Thang SH. 2007. Macromolecules. 40: 4446-4455.


17/19


Polymer architectures through RAFT


18/19


Summary

Powerful tool for controlled free radical polymerisation

living polymerisation 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


19/19


For more informationRAFT Technology Team

CSIRO Materials Science and Engineering

t +61 3 9545 2435

e [email protected] www.csiro.au/products/RAFT

raft choosing the right agent

Documents