investigating nitroxide-mediated radical polymerization of ... · investigating nitroxide-mediated...

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

R 2007

2

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

R 2007

3


Regular Radical Polymerization

Living Ionic Polymerization

Controlled Radical Polymerization

IPR 20

07

4


• Examples of molecular structures attained

IPR 20

07

5

• Applications

– Acrylic block copolymers as stabilizers in coating, ink applications

– Additives suitable for use as components of lubricating oils

– ABC – type block copolymers


IPR 20

07

6


• 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

R 2007

7


• 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)

IPR 20

07

8

• 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)


IPR 20

07

9

FRP

LRP

conversion

nM

termination

living state

slow initiation

ln([

M] 0

/[M

])

time


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

IPR 20

07

10

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)

IPR 20

07

11

• 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

IPR 20

07

12

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

IPR 20

07

13

Side Reactions

• Reaction between TEMPO and BPO

• Nitroxide decomposition

O

N

OO

O OOC

OO C

O O

N+

IPR 20

07

14

Uncertain Aspects (?)

• Initiator efficiency factor (f)

• Uncertain kinetic constants

• Side reactions

IPR 20

07

15

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

IPR 20

07

16

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)

IPR 20

07

17

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

IPR 20

07

18

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

R 2007

19

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

R 2007

20

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)

IPR 20

07

21

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

IPR 20

07

22

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

R 2007

23

• 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

IPR 20

07

24

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

IPR 20

07

25

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

R 2007

26

• 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

IPR 20

07

27

IPR 20

07

28

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.

IPR 20

07

29

n

CH2 CH CH CH NOHn

NCH2 CH CH2 CH Ok decomp +

IPR 20

07

30

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)

IPR 20

07

31

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

]

IPR 20

07

32STY polymerization at 120°C, TEMPO/BPO = 1.1

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

IPR 20

07

33

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

R 2007

34

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

IPR 20

07

35

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

IPR 20

07

36

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

IPR 20

07

37

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)

IPR 20

07

38

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)

IPR 20

07

39

Thermal Self initiation of Styrene

IPR 20

07

40

IPR 20

07

investigating nitroxide-mediated radical polymerization of ... · investigating nitroxide-mediated...

Documents