10.569 Synthesis of Polymers
Prof. Paula Hammond
Lecture 32: Stable Free Radical Polymerization, Atom Transfer Radical
Polymerization, Controlled Free Radical Polymerization
Free radical is most versatile type of chain growth
→
→
Most monomers are available
Can be done in
• emulsion
•
•
suspension
bulk
→ Most robust method: less sensitive to
→
• solvent
• impurity
•
•
atmospheric conditions
Limitations
broad
•
•
lack of control over PDI
difficult to make well defined block copolymers
→ Methods to improve upon traditional free radical
•
•
Stable Free Radical Polymerization (SFRP)
Atom Transfer Radical Polymerization (ATRP)
“Controlled Free Radical Polymerization”
TEMPO → stable nitroxy free radical
N O
Use with initiator that has a fast half life
• Stable free radical must NOT initiate polymerization
• R
SFRcomb
> R p rate of free radical combination
• Need R p
• R t i
<< R
>> R p
, R
SFR
This system first described by
Georges, Veregin, Kazmeier, Homer
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.

Macromolecules, 26, 5316 (1993)
• PDI’s as low as 1.1 – 1.5
• Can form diblocks and triblocks with acrylates and co-monomers (styrene) regardless of addition order!!
• Slow reaction times (30-70 hours)
- rate can be increased with camphor sulfonic acid ( ∼ 6 hours)
• High MWs achievable
• PDI’s narrower for higher ratios of
SFRcomp
• Initiation at high temps lowers PDI
Ri
• Higher temps ⇒
R
R p t
=
⎡ ⎤⎡
⎡ ⋅ ⎤
2
⋅ ⎤
• Reaction has 2 stages
1) TEMPO catalyzed decomposition of BPO
2) Propagation through reversible TEMPO activation/deactivation
- variability in PDI, MW
- different TEMPO/initiator/monomer combinations can yield different results
P n
⋅ + ⋅
T
← ⎯ →
L n
(trapping)
Propagating dissociated trapped “living” chain polymer chain TEMPO or P+T
K
L
= k k
=
L n
⎣
P n
⎦⎣
T ⎤⎦
⎡ P n
⋅ =
L n ≅ constant generally much lower than in traditional free radical
⋅
[ ]
≈
5 %
[ ] o
R trap
= k
⎣ ⎦⎣ n
⋅ >> R p termination rate is much lower
[ n
⋅
]
2 and
R p
∝
[ ] n
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
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Probability of untrapped living chains meeting is very low (termination by combination is negligible).
Kinetics same as previously described.
1.
K
L
= k
L .
f >>
1 .
0
⇒ forward rate is much faster k
L , r
2. Rate of free radical trapping >> propagation rate
3.
R p
>>
R t
(if [M .
] is low, usually true)
Initiation
1.
R
−
X
+
LiM t z
+ ⇔
R
⋅ +
LiM t
( z
+
1 )
+
X
alkyl metal
halide ligand oxidized complex
complex
X = Cl, Br M = Cu, Ni, Pd, Ru, Fe common
2.
R
⋅ +
Propagation
P
N
R'
⎯ ⎯→
P
1
⋅
−
X
+
LiM t z
+ ← ⎯ →
P
N
⋅ +
LiM t
( z
+
1 )
+
X
P
N
⋅ +
R'
⎯ ⎯→
P
N
+
1
⋅
Can use a broad range of catalytic systems.
⇒ Grow a linear polymer from a dendrimer.
⇒ Create a graft copolymer.
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
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⇒ Transfer from ionic polymerization to controlled radical to create block copolymers otherwise inaccessible.
J. Am. Chem. Soc., Vol 118, No 45, 1996
Pg
Dendrimer Block Copolymer
O
O
O
O
O
O
O
O
O
O
O
O
O O
O
O
O
O
O
O
O
O
O
O O
O
O
O
O
O
Br
+
HO
O
N
NaH
O
O
O
O
O
O
O
O
O
O
O
O
O O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
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OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.

Use of Aluminum Alkyls
⇒ low PDI’s, promising approach
N N
THF iBu
2
AlH
N iBu
Al
N iBu iBu iBu iBu
Al
+
N
N
N
N
Al iBu iBu iBu
O
N iBu
+ iBu iBu
N
Al
N
O
N iBu iBu iBu
N
Al
N
O
N
O
MeO
Pol iBu iBu
N
Al
N iBu
MMA O
O N
MeO
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
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OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.

Table 1. Initiating and Terminating Species for Living Radical Polymerizations
I ⋅ X ⋅
1
(C
2
H
5
)
2
NCS
1
SCN(C
2
H
5
)
2 iniferter
S
S
2
(CH
3
)
2
C
H
3
C CH
3
3
(C
6
H
5
CN
)CO
7 O N
O
H
3
C CH
3
4
5
6
C
6
H
5
⋅
CH
O
3
⋅
N
8
ON N
9 Al complexes
H
3
C CH
3
10 O N
Nitroxide
Stable Free
Radicals
O
H
3
C
H
3
C CH
3
CH
3
O
H
3
C CH
3
CO
2
H
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
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OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.

Scheme 2. Living Polymerization of Acrylates and Methacrylates
H
3
C CH
3
CH
3
CH
3
N O
+
H
3
C C N N C CH
3
H
3
C
CH
3
O
H
3
C CH
3
N
CN CN
CN
H
3
C
CH
3
AIBN
H
3
C
CH
3
H
2
C CR
C O
CH
3
H
3
C
CH
3
C CH
2
CH
3
R=H or alkyl
R
C
C O
CH
3
CH
2
H
3
C CH
3
R
C
C O
CH
3 n
CH
2
R
C O
C O
N
CH
3
H
3
C CH
3
Li
O
Si
O
Si O n
Si Si
O
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
Page 7 of 8
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.

Here is an example involving an anionic polymerization that is then end capped with an initiator for ATRP, x-1
OSi O Si O y-1
Si O Si O z-1 excess
O
+
Br Br x-1
OSi O Si O y-1
Si O Si O z-1
O
Pt (catalyst)
Br
+
H
H
3
C
Si R
H
3
C
toluene
60 o
C
R
Si Si
R
O x-1
OSi O Si O y-1
Si O Si O z-1
Br
+
PMDETA (ligand)
CuBr
R
Si
Si
R x-1
OSi O Si O y-1
Si O Si O z-1
O
110 o
C the additional step of hydrosilation of the vinyl groups on the siloxane is not needed for a simple PDMS and would look like: excess x-1
Si O Si O z-1
O
+
Br Br n
Br x-1
Si O Si O z-1
O
Br
+
PMDETA (ligand)
CuBr
110 o
C x-1
Si O Si O z-1
O n
Br
The details for the catalyst and ligand are in the review articles listed below.
Patten, Timothy E., and Krzystof Matyjaszewski. “Atom Transfer Radical
Polymerization and Synthesis of Polymeric Materials.” Advanced Materials 10, no. 12
(1998): 901-915.
Pyun, Jeffrey, Shijun Jia, Tomasz Kowalewski, and Krzystof Matyjaszewski.
“Synthesis and Surface Attachment of ABC Triblock Copolymers Containing Glassy and Rubbery Segments.” Macromol. Chem. Phys.
205 (2004): 411-417.
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
Lecture 32
Page 8 of 8
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.