1
Investigating Nitroxide-Mediated Radical
Polymerization of Styrene over a Range of Reaction Conditions
A. NabifarN. T. McManus
A. PenlidisInstitute for Polymer Research (IPR)Department of Chemical Engineering
University of WaterlooIP
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Controlled Radical Polymerization (CRP)
• (Co) polymers with precisely controlled architectures
• Living Ionic Polymerization (good control but stringent conditions; relatively small number of monomers)
• Regular radical polymerization ( versatile reaction conditions but poor control over some polymer characteristics) IP
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Controlled Radical Polymerization (CRP)
Regular Radical Polymerization
Living Ionic Polymerization
Controlled Radical Polymerization
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Controlled Radical Polymerization (CRP)
• Examples of molecular structures attained
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• Applications
– Acrylic block copolymers as stabilizers in coating, ink applications
– Additives suitable for use as components of lubricating oils
– ABC – type block copolymers
Controlled Radical Polymerization (CRP)
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Controlled Radical Polymerization (CRP)
• Reversible Addition-Fragmentation Transfer (RAFT)
R Br R + CuBr (L) Ka
Kd
+ CuBr2 (L)
• Nitroxide- Mediated Radical Polymerization (NMRP)
• Atom Transfer Radical Polymerization (ATRP)
R R TEMPOKa
Kd
+ TEMPO
SS C
z
R m
S C S
z
R R R + +n m
K exch
nIP
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Controlled Radical Polymerization (CRP)
• Exchange equilibrium favours dormant species
• Concentration of radicals is low; bimolecular termination “almost” negligible
• Radicals grow at the same average rate; low polydispersity product
R X XR+K deact
K act(Active) (Dormant)
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• Prerequisites
– Small contribution of chain – breaking reactions (termination and transfer reactions)
– Fast initiation compared to propagation
– Fast exchange between active and dormant species (provides uniformity in chain length)
Controlled Radical Polymerization (CRP)
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FRP
LRP
conversion
nM
termination
living state
slow initiation
ln([
M] 0
/[M
])
time
Controlled Radical Polymerization (CRP)
• Deviation from linearity can result from slow initiation or loss of radicals by termination
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Nitroxide-Mediated Radical Polymerization(NMRP)
• Addition of a stable nitroxide radical, able to trap the propagating radical in a thermally unstable species
• The most common nitroxide used as trapping agent is TEMPO (2, 2, 6, 6–tetramethyl-1-piperidinyloxy)
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• NMRP of Styrene with BPO and TEMPO
O
O
O
OC
+
STY
k i
Initiation
• Initiator efficiency factor (f)
• (Thermal) Self initiation of Styrene
OO
OO
O
O
2
Benzoyl Peroxide Benzoyloxy radical
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O
O
x
ON
O
O C
n
O N+
k deact
k act
TEMPO
• NMRP of Styrene with BPO and TEMPOO
OC
O
O C
n
+ n
k p
Propagation
• K = kdeact/ kact
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Side Reactions
• Reaction between TEMPO and BPO
• Nitroxide decomposition
O
N
OO
O OOC
OO C
O O
N+
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Uncertain Aspects (?)
• Initiator efficiency factor (f)
• Uncertain kinetic constants
• Side reactions
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Objectives
• Clarify the effect of polymerization conditions (TEMPO/ BPO ratio and temperature )
– Conversion (rate)– Molecular weights – Polydispersity
• Generate a source of reliable experimental data
– Validation of mathematical models – Parameter estimation– Identification of optimal polymerization conditions
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Summary of Runs
1.50.036
120
130
+ Replicate
Styrene with unimolecular initiator
Styrene with TEMPO only
Thermal (self) initiation of styrene+ Replicate
+ Replicate
+ Replicate
-
-
1.3
1.1
-
1.2
1.1
Nil
Nil
0.036
0.036
Nil
0.036
0.036
0.90.036
0.90.036
Remarks[TEMPO] / [BPO][BPO] 0M
Temperature(°C)
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80Time, t (hr)
Con
vers
ion,
X
TEMPO/BPO=0.9
TEMPO/BPO = 1.1
TEMPO/BPO=1.1,Independent replicate
TEMPO/BPO = 1.2
TEMPO/BPO = 1.5
Effect of TEMPO/BPO Ratio
STY polymerization at 120 °C, [BPO] 0 = 0.036 M
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
0 0.2 0.4 0.6 0.8 1Conversion, X
Wei
ght A
vera
ge M
olec
ular
Wei
ght (
gr/m
ol)
TEMPO/BPO=0.9
TEMPO/BPO=1.1
TEMPO/BPO=1.2
TEMPO/BPO=1.5
STY polymerization at 120º C, [BPO] 0 = 0.036 MIP
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0
1
2
3
4
5
6
7
8
9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Conversion,X
Poly
disp
ersi
ty, P
DI
TEMPO/BPO=0.9
TEMPO/BPO=1.1
TEMPO/BPO=1.2
TEMPO/BPO=1.5
STY polymerization at 120º C, [BPO] 0 = 0.036 MIP
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Observations
• The larger the TEMPO/ BPO ratio (the more TEMPO in the recipe), the slower the polymerization
• Higher values of average molecular weights, Mn and Mw, are obtained as TEMPO/BPO ratio decreases
• Low PDI values, below 1.2
• Similar trends with experimental data at 130°C (not shown)
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80Time, t (hr)
Con
vers
ion,
X
130120
STY polymerization at TEMPO / BPO = 0.9
Effect of Temperature
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000W
eigh
t Ave
rage
Mol
ecul
ar W
eigh
t (gr
/mol
)
T = 130T = 120T = 120 ,Independent replicate
1
1.2
1.4
1.6
1.8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Conversion, X
PDI
STY polymerization at TEMPO / BPO = 0.9IP
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• Kinetic model based on a detailed reaction mechanism
• Molar balances; population balances; set of ordinary differential equations
• General trends OK
• Satisfactory prediction of experimental data but more work needs to be done ( fine-tuning of key but uncertain parameters)
Mathematical Modeling
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Concluding Remarks
• “Optimal” ratio to achieve lowest polydispersity seems to be around [TEMPO]/ [BPO] = 1.2
• There is no pronounced temperature effect at studied conditions
• Model trends and preliminary predictions satisfactory for typical polymerization variables (on going work)
1
1.1
1.2
1.3
1.4
1.5
0.9 1.1 1.2 1.5TEMPO/BPO Ratio
PDI
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Future Steps• Experimental :
– Comparison with unimolecular initiator– Different initiator (tetrafunctional vs. monofunctional
initiator)
• Modeling :
– More rigorous parameter estimation
– Using Bayesian design to guide our experimentation for better understanding of the reaction mechanismIP
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• NSERC CRO Grant
• OGSST – OMNOVA Solutions
• Canada Research Chair (CRC) program ( A. Penlidis)
• CRO grant is a collaborative effort under an Inter -American Materials Collaboration ( IAMC ) joint project with Prof. E. Vivaldo-Lima, M. Roa-Luna ( UNAM, Mexico ) and Prof. L. M.F. Lona,J.B. Ximenes ( Campinas, Brazil )
Acknowledgements
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References• Handbook of Radical Polymerization. Matyjaszewski, K., and Davis, T.P.,
Eds. Wiley-Interscience: Hoboken, 2002.
• Georges, M.K., Veregin, R.P.N., Kazmaier, P.M., and Hamer, G.K. (1993) Macromolecules, 26 (11): 2987-2988.
• Greszta, D. and Matyjaszewski, K. (1996) Macromolecules, 29: 7661-7670.
• MacLeod, P. J. , Veregin R.P.N., Odell, P.G., and Georges, M.K. (1997) Macromolecules, 30 :2207-2208.
• Bonilla, J., Saldívar, E., Flores-Tlacuahuac, A., Vivaldo-Lima, E., Pfaendner, R., and Tiscareño-Lechuga, F. (2002) Polym. React. Eng. J., 10 (4): 227-263.
• Goto, A. and Fukuda, T. (2004) Prog. Polym. Sci., 29: 329–385.
• Roa- Luna, M., Nabifar, A., Diaz-Barber, M. P., McManus, N.T., Vivaldo-Lima, E., Lona, L.M.F., and Penlidis, A. (2007) J. Macromol. Sci., A: Pure Appl. Chem., A44: 337-349.
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n
CH2 CH CH CH NOHn
NCH2 CH CH2 CH Ok decomp +
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Experimental
• Polymerization
– Ampoules (~ 4ml volume): degassed , torch-sealed, and then placed in liquid nitrogen until used
– Isothermal oil bath
• Polymer Characterization
– Monomer conversion • Gravimetry
– Molecular weight averages and polydispersity • Gel permeation chromatography (GPC)
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60
Time, t (hr)
Con
vers
ion,
X
Replicate
STY polymerization at 120°C, TEMPO/BPO = 1.1
Results
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35Time, t (hr)
Ln [M
] 0/[M
]
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0
5,000
10,000
15,000
20,000
25,000
30,000A
vera
ge M
olec
ular
Wei
ghts
(gr/m
ol)
MnMw
1
1.2
1.4
1.6
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Conversion, X
PDI
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Remarks
• As expected, polymerization proceeds faster at the higher temperature
– After about 80-85% conversion, rates are almost identical for both temperatures
• A small reduction in molecular weight values as temperature increases
• Experimental data also available for TEMPO/ BPO=1.1IP
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20 25 30 35 40Time, t (hr)
Con
vers
ion,
X
Experimental data
Predicted Profile
STY polymerization at T = 130 °C ,TEMPO/BPO = 1.1
Mathematical Modeling
0
5000
10000
15000
20000
25000
30000
35000
0.0 0.2 0.4 0.6 0.8 1.0
Conversion, X
Num
ber A
vera
ge M
olec
ular
Wei
ght (
g/m
ol) Experimental data
Predicted Profile
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STY polymerization at T = 130 °C ,TEMPO/BPO = 1.1
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
0 0.2 0.4 0.6 0.8 1Conversion, X
PD
IExperimental data
Predicted Profile
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0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.022
0.024
1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02
Time (hr)
Con
cent
ratio
n, m
ol/L
[I]
[NOx*]
[NOe]
Typical calculated profiles for concentration of initiator, nitroxylstable radicals and alcoxyamine
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Description Step
Chemical initiation 2dkinI R⎯⎯→ •
Nitroxyl ether decomposition 2
2
⎯⎯⎯→
←⎯⎯ • + •ka
dE in xkNO R NO
Mayo dimerization dim+ ⎯⎯→kM M D
Thermal initiation i+ ⎯⎯→ •+ •akM D D M
First propagation (primary radicals) 1•+ ⎯⎯→ •pk
inR M R
First propagation (monomeric radicals) 1
pkM M R•+ ⎯⎯→ •
First propagation (dimeric radicals) 1pkD M R• + ⎯⎯→ •
Propagation 1
pkr rR M R +• + ⎯⎯→ •
Dormant living exchange (monomeric alkoxyamine) ←⎯⎯
•+ • ⎯⎯→ka
dax xkM NO MNO
Dormant living exchange (polymeric alkoxyamine) ←⎯⎯
•+ •⎯⎯→ka
dar x r xkR NO R NO
Alkoxyamine decomposition ⎯⎯⎯→ +decompkx xMNO M HNO
Rate enhancement reaction 3+ •⎯⎯→ •+hkx xD NO D HNO
Termination by combination tckr s r sR R P +• + • ⎯⎯→
Termination by disproportionation tdkr s r sR R P P•+ •⎯⎯→ +
Transfer to monomer fMkr rR M P M• + ⎯⎯→ + •
Transfer to dimer fDkr rR D P D• + ⎯⎯→ + •
Kin
etic
Mec
hani
sm
(Bon
illa
et a
l., 2
002)
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Description Step
Chemical initiation 2dkinI R⎯⎯→ •
Nitroxyl ether decomposition 2
2
⎯⎯⎯→
←⎯⎯ • + •ka
dE in xkNO R NO
Mayo dimerization dim+ ⎯⎯→kM M D
Thermal initiation i+ ⎯⎯→ •+ •akM D D M
First propagation (primary radicals) 1•+ ⎯⎯→ •pk
inR M R
First propagation (monomeric radicals) 1
pkM M R•+ ⎯⎯→ •
First propagation (dimeric radicals) 1pkD M R• + ⎯⎯→ •
Propagation 1
pkr rR M R +• + ⎯⎯→ •
Dormant living exchange (monomeric alkoxyamine) ←⎯⎯
•+ • ⎯⎯→ka
dax xkM NO MNO
Dormant living exchange (polymeric alkoxyamine) ←⎯⎯
•+ •⎯⎯→ka
dar x r xkR NO R NO
Alkoxyamine decomposition ⎯⎯⎯→ +decompkx xMNO M HNO
Rate enhancement reaction 3+ •⎯⎯→ •+hkx xD NO D HNO
Termination by combination tckr s r sR R P +• + • ⎯⎯→
Termination by disproportionation tdkr s r sR R P P•+ •⎯⎯→ +
Transfer to monomer fMkr rR M P M• + ⎯⎯→ + •
Transfer to dimer fDkr rR D P D• + ⎯⎯→ + •
Kin
etic
Mec
hani
sm
(Bon
illa
et a
l., 2
002)
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Thermal Self initiation of Styrene
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