Presentation (PDF) - University of Waterloo

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Investigating Nitroxide-Mediated Radical Polymerization of Styrene over a Range of Reaction Conditions

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A. Nabifar N. T. McManus A. Penlidis Institute for Polymer Research (IPR) Department of Chemical Engineering University of Waterloo 1

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Controlled Radical Polymerization (CRP)

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• (Co) polymers with precisely controlled architectures

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• Living Ionic Polymerization (good control but stringent conditions; relatively small number of monomers)

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• Regular radical polymerization ( versatile reaction conditions but poor control over some polymer characteristics)

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Regular Radical Polymerization

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Controlled Radical Polymerization (CRP)

Living Ionic Polymerization

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Controlled Radical Polymerization

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Controlled Radical Polymerization (CRP)

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• Examples of molecular structures attained

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Controlled Radical Polymerization (CRP)

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• Applications

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– Acrylic block copolymers as stabilizers in coating, ink applications

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– Additives suitable for use as components of lubricating oils – ABC – type block copolymers

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Controlled Radical Polymerization (CRP)

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• Nitroxide- Mediated Radical Polymerization (NMRP) Ka

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R + TEMPO

TEMPO

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Kd

• Atom Transfer Radical Polymerization (ATRP) Ka

R

Br + CuBr (L)

R

+ CuBr2 (L)

Kd

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• Reversible Addition-Fragmentation Transfer (RAFT) R +S m

K exch

C z

S

R

n

R

m

S

C

S+ R

n

z 6

Controlled Radical Polymerization (CRP) K deact

+ X

R

K act

(Dormant)

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(Active)

X

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R

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• Exchange equilibrium favours dormant species

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• Concentration of radicals is low; bimolecular termination “almost” negligible • Radicals grow at the same average rate; low polydispersity product 7

Controlled Radical Polymerization (CRP)

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• Prerequisites

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– Small contribution of chain – breaking reactions (termination and transfer reactions)

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– Fast initiation compared to propagation

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– Fast exchange between active and dormant species (provides uniformity in chain length)

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Mn

termination

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slow initiation

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living state

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ln([M]0 /[M])

Controlled Radical Polymerization (CRP)

FRP

LRP

time

conversion

• Deviation from linearity can result from slow initiation or loss of radicals by termination 9

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Nitroxide-Mediated Radical Polymerization (NMRP)

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• Addition of a stable nitroxide radical, able to trap the propagating radical in a thermally unstable species

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• 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

O

O

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Benzoyl Peroxide O

ki

Initiation

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+

O

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2

O

Benzoyloxy radical O

O

C

STY

• Initiator efficiency factor (f) • (Thermal) Self initiation of Styrene 11

• NMRP of Styrene with BPO and TEMPO O

+

n

Propagation

O

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C

C n

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O

O

kp

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O O

+

O

O

N

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C

k deact

n

TEMPO

N

k act

O

O x

• K = kdeact/ kact 12

Side Reactions

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• Reaction between TEMPO and BPO +

N O

O

O

O

O

C

O

O

O O

O

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C

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N

• Nitroxide decomposition

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Uncertain Aspects (?)

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• Initiator efficiency factor (f)

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• Side reactions

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• Uncertain kinetic constants

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Objectives

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– Conversion (rate) – Molecular weights – Polydispersity

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• Clarify the effect of polymerization conditions (TEMPO/ BPO ratio and temperature )

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• Generate a source of reliable experimental data – Validation of mathematical models – Parameter estimation – Identification of optimal polymerization conditions 15

Summary of Runs [BPO] 0 M

[TEMPO] / [BPO]

120

0.036

0.9

0.036

1.1

0.036

1.2 1.5 -

0.036

0.9

R

Nil

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130

+ Replicate

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0.036

Remarks

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Temperature (°C)

Styrene with unimolecular initiator

0.036

1.1

+ Replicate

0.036

1.3

+ Replicate

Nil

-

Thermal (self) initiation of styrene + Replicate

Nil

-

Styrene with TEMPO only 16

Effect of TEMPO/BPO Ratio 1 0.9

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0.8

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0.6 0.5 0.4

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TEMPO/BPO=0.9

0.3 0.2

TEMPO/BPO = 1.1 TEMPO/BPO=1.1,Independent replicate

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Conversion, X

0.7

0.1

TEMPO/BPO = 1.2 TEMPO/BPO = 1.5

0 0

10

20

30

40

50

60

70

80

Time, t (hr)

STY polymerization at 120 °C, [BPO] 0 = 0.036 M

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35,000 30,000

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25,000 20,000

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15,000 10,000

TEMPO/BPO=0.9 TEMPO/BPO=1.1

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Weight Average Molecular Weight (gr/mol)

40,000

5,000 0 0

0.2

TEMPO/BPO=1.2 TEMPO/BPO=1.5

0.4

0.6

0.8

1

Conversion, X

STY polymerization at 120º C, [BPO] 0 = 0.036 M 18

9 TEMPO/BPO=0.9

8

TEMPO/BPO=1.1 TEMPO/BPO=1.2

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7

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6 5 4

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3 2

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Polydispersity, PDI

TEMPO/BPO=1.5

1 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Conversion,X

STY polymerization at 120º C, [BPO] 0 = 0.036 M

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Observations

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• The larger the TEMPO/ BPO ratio (the more TEMPO in the recipe), the slower the polymerization

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• Higher values of average molecular weights, Mn and Mw, are obtained as TEMPO/BPO ratio decreases

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• Low PDI values, below 1.2 • Similar trends with experimental data at 130°C (not shown) 20

Effect of Temperature 1

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0.9 0.8

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0.6 0.5

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0.4 0.3 0.2

130 120

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Conversion, X

0.7

0.1 0 0

10

20

30

40

50

60

70

80

Time, t (hr)

STY polymerization at TEMPO / BPO = 0.9

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35,000 30,000

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25,000 20,000

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15,000 10,000 5,000 0

1.8

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1.6 PDI

T = 130 T = 120 T = 120 ,Independent replicate

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Weight Average Molecular Weight (gr/mol)

40,000

1.4 1.2 1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Conversion, X

STY polymerization at TEMPO / BPO = 0.9 22

Mathematical Modeling

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• Kinetic model based on a detailed reaction mechanism

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• Molar balances; population balances; set of ordinary differential equations

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• General trends OK

• Satisfactory prediction of experimental data but more work needs to be done ( fine-tuning of key but uncertain parameters) 23

Concluding Remarks 1.5

1.3

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PDI

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• “Optimal” ratio to achieve lowest polydispersity seems to be around [TEMPO]/ [BPO] = 1.2

1.4

1.2

1.1

1 0.9

1.1 1.2 TEMPO/BPO Ratio

1.5

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• There is no pronounced temperature effect at studied conditions • Model trends and preliminary predictions satisfactory for typical polymerization variables (on going work)

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Future Steps • Experimental :

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– Comparison with unimolecular initiator

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• Modeling :

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– Different initiator (tetrafunctional vs. monofunctional initiator)

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– More rigorous parameter estimation – Using Bayesian design to guide our experimentation for better understanding of the reaction mechanism

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Acknowledgements

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• NSERC CRO Grant

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• OGSST – OMNOVA Solutions

• Canada Research Chair (CRC) program ( A. Penlidis)

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• 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 )

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References Handbook of Radical Polymerization. Matyjaszewski, K., and Davis, T.P., Eds. Wiley-Interscience: Hoboken, 2002.

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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: 76617670.

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MacLeod, P. J. , Veregin R.P.N., Odell, P.G., and Georges, M.K. (1997) Macromolecules, 30 :2207-2208.

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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., VivaldoLima, E., Lona, L.M.F., and Penlidis, A. (2007) J. Macromol. Sci., A: Pure Appl. Chem., A44: 337-349.

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•

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k decomp

N

CH2

CH

CH

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O

CH + HO

N

n

20

n

CH2 CH

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CH

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CH2

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Experimental • Polymerization

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– Ampoules (~ 4ml volume): degassed , torch-sealed, and then placed in liquid nitrogen until used – Isothermal oil bath

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• Polymer Characterization

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– Monomer conversion • Gravimetry

– Molecular weight averages and polydispersity • Gel permeation chromatography (GPC) 30

Results 1 0.9 0.8

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0.6 0.5 0.4

2.5

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0.3 0.2 0.1

2

0 10

20

30 Time, t (hr)

40

50

60

R

0

Ln [M]0/[M]

Replicate

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Conversion, X

0.7

1.5

1

0.5

0 0

5

10

15

20

25

30

35

Time, t (hr)

STY polymerization at 120°C, TEMPO/BPO = 1.1

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25,000

07

20,000 15,000 10,000 5,000 0

R

1.6

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1.4 PDI

Mn Mw

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Average Molecular Weights (gr/mol)

30,000

1.2 1 0.0

0.1

0.2

0.3

0.4 0.5 0.6 Conversion, X

0.7

0.8

0.9

STY polymerization at 120°C, TEMPO/BPO = 1.1

1.0

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Remarks

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• As expected, polymerization proceeds faster at the higher temperature

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– After about 80-85% conversion, rates are almost identical for both temperatures

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• A small reduction in molecular weight values as temperature increases • Experimental data also available for TEMPO/ BPO=1.1

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Mathematical Modeling 1 0.9 0.8

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0.6 0.5

35000

0.3 0.2

Experimental data

0.1

Predicted Profile

0 5

10

15

20 Time, t (hr)

25

30

35

40

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0

Number Average Molecular Weight (g/mol)

20

0.4

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Conversion, X

0.7

30000

Experimental data

Predicted Profile

25000 20000 15000 10000 5000

0 0.0

0.2

0.4

0.6

0.8

1.0

Conversion, X

STY polymerization at T = 130 °C ,TEMPO/BPO = 1.1

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6 Experimental data

5.5

Predicted Profile

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5 4.5

20

3.5 3

R

2.5 2 1.5 1 0

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PDI

4

0.2

0.4 0.6 Conversion, X

0.8

1

STY polymerization at T = 130 °C ,TEMPO/BPO = 1.1 35

0.024 0.022 0.02

07

0.016

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0.014 0.012 0.01

R

0.008 0.006 0.004 0.002

[I]

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Concentration, mol/L

0.018

[NOx*] [NOe]

0 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)

Typical calculated profiles for concentration of initiator, nitroxyl stable radicals and alcoxyamine

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Description

d I ⎯ k⎯ → 2 Rin •

Chemical initiation Nitroxyl ether decomposition

ka 2 ⎯⎯⎯ →

NOE ←⎯⎯ Rin • + NO x • kd 2 d im M + M ⎯ k⎯ →D

Thermal initiation

ki a M + D ⎯⎯ → D •+M •

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Mayo dimerization

p Rin • + M ⎯⎯ → R1 •

First propagation (monomeric radicals)

p M • + M ⎯⎯ → R1 •

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First propagation (primary radicals)

First propagation (dimeric radicals) Propagation

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Dormant living exchange (monomeric alkoxyamine) Dormant living exchange (polymeric alkoxyamine)

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Kinetic Mechanism (Bonilla et al., 2002)

Step

Alkoxyamine decomposition Rate enhancement reaction Termination by combination Termination by disproportionation Transfer to monomer Transfer to dimer

k

k

p D • + M ⎯⎯ → R1 •

k

p Rr • + M ⎯ ⎯ → R r +1 •

k

ka ←⎯⎯

M • + NOx • ⎯⎯ → MNOx k da a ←⎯⎯ k

Rr • + NOx • ⎯⎯ → Rr NOx kda decomp MNOx ⎯⎯⎯ → M + HNOx

k

kh 3 D + NOx • ⎯⎯ → D • + HNOx ktc Rr • + Rs • ⎯⎯ → Pr + s

ktd Rr • + Rs • ⎯⎯ → Pr + Ps fM Rr • + M ⎯⎯→ Pr + M •

k

fD Rr • + D ⎯⎯→ Pr + D •

k

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Description

d I ⎯ k⎯ → 2 Rin •

Chemical initiation Nitroxyl ether decomposition

ka 2 ⎯⎯⎯ →

NOE ←⎯⎯ Rin • + NO x • kd 2 d im M + M ⎯ k⎯ →D

Thermal initiation

ki a M + D ⎯⎯ → D •+M •

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Mayo dimerization

p Rin • + M ⎯⎯ → R1 •

First propagation (monomeric radicals)

p M • + M ⎯⎯ → R1 •

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First propagation (primary radicals)

First propagation (dimeric radicals) Propagation

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Dormant living exchange (monomeric alkoxyamine) Dormant living exchange (polymeric alkoxyamine)

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Kinetic Mechanism (Bonilla et al., 2002)

Step

Alkoxyamine decomposition Rate enhancement reaction Termination by combination Termination by disproportionation Transfer to monomer Transfer to dimer

k

k

p D • + M ⎯⎯ → R1 •

k

p Rr • + M ⎯ ⎯ → R r +1 •

k

ka ←⎯⎯

M • + NOx • ⎯⎯ → MNOx k da a ←⎯⎯ k

Rr • + NOx • ⎯⎯ → Rr NOx kda decomp MNOx ⎯⎯⎯ → M + HNOx

k

kh 3 D + NOx • ⎯⎯ → D • + HNOx ktc Rr • + Rs • ⎯⎯ → Pr + s

ktd Rr • + Rs • ⎯⎯ → Pr + Ps fM Rr • + M ⎯⎯→ Pr + M •

k

fD Rr • + D ⎯⎯→ Pr + D •

k

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R

20

07

Thermal Self initiation of Styrene

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40

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