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					         Investigating
  Nitroxide-Mediated Radical




                     07
Polymerization of Styrene over a
 Range of Reaction Conditions


              20
                    A. Nabifar
        R
                 N. T. McManus
    IP
                    A. Penlidis
     Institute for Polymer Research (IPR)
     Department of Chemical Engineering
             University of Waterloo

                                            1
Controlled Radical Polymerization (CRP)




                             07
• (Co) polymers with precisely controlled architectures




                       20
• Living Ionic Polymerization (good control but stringent
  conditions; relatively small number of monomers)
                 R
• Regular radical polymerization ( versatile reaction
            IP
  conditions but poor control over some polymer
  characteristics)


                                                            2
Controlled Radical Polymerization (CRP)




                               07
      Regular Radical                         Living Ionic
      Polymerization                         Polymerization




                        20
               R        Controlled Radical
                         Polymerization
        IP


                                                              3
Controlled Radical Polymerization (CRP)

• Examples of molecular structures attained




                           07
                     20
                R
           IP


                                              4
Controlled Radical Polymerization (CRP)

• Applications




                             07
   – Acrylic block copolymers as stabilizers in coating,
     ink applications




                      20
   – Additives suitable for use as components of
                 R
     lubricating oils
           IP
   – ABC – type block copolymers



                                                           5
Controlled Radical Polymerization (CRP)

• Nitroxide- Mediated Radical Polymerization (NMRP)




                                     07
                                     Ka
               R       TEMPO                   R + TEMPO
                                     Kd




                            20
• Atom Transfer Radical Polymerization (ATRP)
                                          Ka
           R       Br + CuBr (L)
                   R                                   R   + CuBr2 (L)
                                          Kd
           IP
• Reversible Addition-Fragmentation Transfer (RAFT)
                                    K exch
      R +S         C    S   R                  R           S   C    S+ R
       m                        n                  m                       n


                   z                                           z
                                                                               6
Controlled Radical Polymerization (CRP)

                            K deact
                  R   + X             R     X




                            07
                            K act
               (Active)               (Dormant)




                          20
• Exchange equilibrium favours dormant species
                R
• Concentration of radicals is low; bimolecular termination
  “almost” negligible
           IP

• Radicals grow at the same average rate; low
  polydispersity product

                                                          7
Controlled Radical Polymerization (CRP)

• Prerequisites




                            07
   – Small contribution of chain – breaking reactions




                      20
     (termination and transfer reactions)

   – Fast initiation compared to propagation
                  R
   – Fast exchange between active and dormant species
           IP
     (provides uniformity in chain length)



                                                        8
                Controlled Radical Polymerization (CRP)

                                                     Mn
ln([M]0 /[M])




                                                     07
                                   living
                                   state

                                                          FRP




                                              20
                                termination


                                        R                 LRP
                     slow initiation
                             IP
                                              time
                                                                conversion

       • Deviation from linearity can result from slow initiation
       or loss of radicals by termination
                                                                         9
Nitroxide-Mediated Radical Polymerization
                 (NMRP)




                               07
• Addition of a stable nitroxide radical, able to trap the




                        20
  propagating radical in a thermally unstable species

• The most common nitroxide used as trapping agent is
                  R
  TEMPO (2, 2, 6, 6–tetramethyl-1-piperidinyloxy)
             IP


                                                             10
• NMRP of Styrene with BPO and TEMPO
                    O   O
                                                          O

                                                2




                                  07
                   O    O
                                                          O

          Benzoyl Peroxide                     Benzoyloxy radical




                            20
                O                                         O
                                    ki
                        +
                        R         Initiation              O
               O
                                                              C
            IP
                            STY


• Initiator efficiency factor (f)
• (Thermal) Self initiation of Styrene
                                                                    11
• NMRP of Styrene with BPO and TEMPO
            O
                                            kp             O
                        +   n
            O                           Propagation        O




                                            07
                                                                       C
                C
                                                                   n




                                    20
         O              R                              O
                                             k deact
        O
                        C   +   O   N                                  N
                                                                   O
                IP
                    n
                                              k act    O

                                                               x
                                    TEMPO




• K = kdeact/ kact
                                                                           12
Side Reactions

• Reaction between TEMPO and BPO




                               07
                                       +
               N                       N




                           20
               O                       O
       O                   O
                               O               O
           C   O   O   C           O       O
                   R
           IP
• Nitroxide decomposition



                                                   13
Uncertain Aspects (?)

• Initiator efficiency factor (f)




                                07
• Uncertain kinetic constants




                         20
• Side reactions   R
             IP


                                     14
Objectives

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




                             07
   – Conversion (rate)




                      20
   – Molecular weights
   – Polydispersity
                 R
• Generate a source of reliable experimental data
           IP
   – Validation of mathematical models
   – Parameter estimation
   – Identification of optimal polymerization conditions

                                                            15
Summary of Runs
 Temperature   [BPO] 0   [TEMPO] / [BPO]               Remarks
    (°C)         M




                                     07
    120        0.036           0.9

               0.036           1.1                    + Replicate




                          20
               0.036           1.2

               0.036           1.5

                 Nil
                   R            -          Styrene with unimolecular initiator
    130        0.036           0.9
               IP
               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

                   0.8




                                               07
                   0.7
   Conversion, X




                   0.6




                                        20
                   0.5

                   0.4
                                   R                 TEMPO/BPO=0.9
                   0.3                               TEMPO/BPO = 1.1

                   0.2                               TEMPO/BPO=1.1,Independent replicate
                             IP
                                                     TEMPO/BPO = 1.2
                   0.1
                                                     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                        17
                                           40,000

                                           35,000
Weight Average Molecular Weight (gr/mol)




                                                                               07
                                           30,000

                                           25,000




                                                                     20
                                           20,000

                                           15,000

                                           10,000
                                                               R                           TEMPO/BPO=0.9
                                                                                           TEMPO/BPO=1.1
                                                         IP
                                                                                           TEMPO/BPO=1.2
                                            5,000
                                                                                           TEMPO/BPO=1.5

                                               0
                                                    0          0.2       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
                      7




                                                         07
                                                                           TEMPO/BPO=1.5
Polydispersity, PDI




                      6




                                               20
                      5

                      4

                      3                R
                      2
                               IP
                      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
                                                                                               19
Observations

• The larger the TEMPO/ BPO ratio (the more TEMPO in




                             07
  the recipe), the slower the polymerization




                       20
• Higher values of average molecular weights, Mn and
  Mw, are obtained as TEMPO/BPO ratio decreases
                 R
• Low PDI values, below 1.2
            IP

• Similar trends with experimental data at 130°C (not
  shown)
                                                        20
Effect of Temperature
                    1

                   0.9




                                                    07
                   0.8

                   0.7
   Conversion, X




                   0.6




                                          20
                   0.5

                   0.4

                   0.3
                                    R
                   0.2                                                       130
                              IP
                   0.1                                                       120

                    0
                         0     10    20   30       40         50   60   70         80
                                               Time, t (hr)

                             STY polymerization at TEMPO / BPO = 0.9                    21
Weight Average Molecular Weight (gr/mol)
                                           40,000

                                           35,000

                                           30,000

                                           25,000




                                                                                  07
                                           20,000

                                           15,000




                                                                      20
                                           10,000                                                     T = 130
                                                                                                      T = 120
                                            5,000                                                     T = 120 ,Independent replicate

                                               0

                                              1.8
                                              1.6
                                                              R
                PDI




                                                        IP
                                              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

• Kinetic model based on a detailed reaction mechanism




                            07
• Molar balances; population balances; set of ordinary




                      20
  differential equations

• General trends OK
                 R
           IP
• Satisfactory prediction of experimental data but more
  work needs to be done ( fine-tuning of key but uncertain
  parameters)

                                                         23
Concluding Remarks
                                         1.5


                                         1.4

• “Optimal” ratio to achieve
                                         1.3




                             07
  lowest polydispersity seems to




                                   PDI
  be around [TEMPO]/ [BPO] =             1.2



  1.2                                    1.1




                      20
                                          1
                                               0.9    1.1       1.2    1.5
                                                     TEMPO/BPO Ratio



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


                                                                             24
Future Steps
• Experimental :
   – Comparison with unimolecular initiator




                              07
   – Different initiator (tetrafunctional vs. monofunctional
     initiator)




                       20
• Modeling :
                   R
   – More rigorous parameter estimation
            IP
   – Using Bayesian design to guide our experimentation
     for better understanding of the reaction mechanism



                                                               25
Acknowledgements
• NSERC CRO Grant




                           07
• OGSST – OMNOVA Solutions




                     20
• Canada Research Chair (CRC) program ( A. Penlidis)

• CRO grant is a collaborative effort under an Inter -
                R
  American Materials Collaboration ( IAMC ) joint project
  with Prof. E. Vivaldo-Lima, M. Roa-Luna
          IP
  ( UNAM, Mexico ) and Prof. L. M.F. Lona,
  J.B. Ximenes ( Campinas, Brazil )


                                                        26
     IP
       R
           20
                07
27
                           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.




                                    07
    (1993) Macromolecules, 26 (11): 2987-2988.

•   Greszta, D. and Matyjaszewski, K. (1996) Macromolecules, 29: 7661-
    7670.




                           20
•   MacLeod, P. J. , Veregin R.P.N., Odell, P.G., and Georges, M.K. (1997)
    Macromolecules, 30 :2207-2208.

•
                    R
    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.
             IP
•   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.
                                                                          28
                                k decomp
CH2   CH       CH2 CH   O   N              CH2   CH       CH   CH + HO   N




                                      07
           n                                          n




                                20
                        R
               IP


                                                                             29
 Experimental
• Polymerization

   – Ampoules (~ 4ml volume): degassed , torch-sealed,




                             07
     and then placed in liquid nitrogen until used




                       20
   – Isothermal oil bath

• Polymer Characterization
                   R
   – Monomer conversion
            IP
      • Gravimetry

   – Molecular weight averages and polydispersity
      • Gel permeation chromatography (GPC)
                                                         30
            Results
                 1

                0.9

                0.8

                0.7
Conversion, X




                                                                           07
                0.6

                0.5

                0.4

                0.3                                                                      2.5




                                                         20
                0.2

                0.1                                                                       2
                                                          Replicate
                 0
                      0   10    20       30         40   50           60




                                                                           Ln [M]0/[M]
                                                    R                                    1.5
                                     Time, t (hr)

                                                                                          1
                                     IP
                                                                                         0.5



                                                                                          0
                                                                                               0   5   10   15        20   25   30        35
                                                                                                            Time, t (hr)


                               STY polymerization at 120°C, TEMPO/BPO = 1.1
                                                                                                                                     31
Average Molecular Weights (gr/mol)
                                     30,000

                                     25,000

                                     20,000




                                                                            07
                                     15,000

                                     10,000
                                                                                                               Mn




                                                                  20
                                      5,000                                                                    Mw

                                          0
                                         1.6

                                         1.4
                                                           R
PDI




                                                     IP
                                         1.2

                                          1
                                               0.0   0.1   0.2   0.3   0.4    0.5      0.6   0.7   0.8   0.9        1.0
                                                                          Conversion, X



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

• As expected, polymerization proceeds faster at the




                            07
  higher temperature

   – After about 80-85% conversion, rates are almost




                      20
     identical for both temperatures
                R
• A small reduction in molecular weight values as
  temperature increases
           IP

• Experimental data also available for TEMPO/ BPO=1.1


                                                        33
                  Mathematical Modeling
                 1

                0.9

                0.8

                0.7




                                                                                     07
Conversion, X




                0.6

                0.5

                0.4
                                                                                                                               35000
                                                                                                                                         Experimental data




                                                                           20        Number Average Molecular Weight (g/mol)
                0.3
                                                                                                                               30000     Predicted Profile
                0.2                                         Experimental data

                0.1                                         Predicted Profile                                                  25000
                 0
                      0   5   10   15       20         25   30
                                                            R            35     40                                             20000
                                        Time, t (hr)
                                                                                                                               15000
                                          IP
                                                                                                                               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                                                                                                       34
       6
                                                  Experimental data
      5.5
                                                  Predicted Profile
       5




                                   07
      4.5

       4
PDI




                            20
      3.5

       3

      2.5             R
       2
                IP
      1.5

       1
            0        0.2       0.4          0.6    0.8                1
                                Conversion, X

            STY polymerization at T = 130 °C ,TEMPO/BPO = 1.1
                                                                          35
                       0.024

                       0.022

                        0.02

                       0.018




                                                                                    07
Concentration, mol/L




                       0.016

                       0.014




                                                                  20
                       0.012

                        0.01

                       0.008

                       0.006

                       0.004          [I]
                                                      R
                                        IP
                                      [NOx*]
                       0.002
                                      [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                                                                                    36
                                                Description                                 Step

                         Chemical initiation                                       →
                                                                            I ⎯ k⎯ 2 Rin •
                                                                                 d




                         Nitroxyl ether decomposition                              ⎯⎯⎯
                                                                                    ka 2
                                                                                         →
                                                                            NOE ←⎯⎯ Rin • + NO x •
                                                                                 kd 2



                         Mayo dimerization                                  M + M ⎯ k⎯ → D
                                                                                     d im
(Bonilla et al., 2002)
Kinetic Mechanism


                         Thermal initiation                                             →
                                                                            M + D ⎯⎯ D •+M •
                                                                                   ki a




                                                          07
                                                                                         →
                                                                            Rin • + M ⎯⎯ R1 •
                                                                                            k
                         First propagation (primary radicals)                          p




                                                                                       →
                                                                            M • + M ⎯⎯ R1 •
                                                                                        k
                         First propagation (monomeric radicals)                      p




                                                                                       →
                                                                            D • + M ⎯⎯ R1 •
                                                                                        k




                                              20
                         First propagation (dimeric radicals)                        p




                                                                                           →
                                                                             R r • + M ⎯ ⎯ R r +1 •
                                                                                                k
                         Propagation                                                     p




                         Dormant living exchange (monomeric alkoxyamine)                        ←⎯⎯
                                                                                                 ka


                              R                                                               →
                                                                            M • + NOx • ⎯⎯ MNOx
                                                                                         k da



                         Dormant living exchange (polymeric alkoxyamine)                        ←⎯⎯
                                                                                                  a k

                                                                                              →
                                                                            Rr • + NOx • ⎯⎯ Rr NOx
                                                                                          kda
                         IP
                                                                                        →
                                                                           MNOx ⎯⎯⎯ M + HNOx
                                                                                    k
                         Alkoxyamine decomposition                               decomp




                         Rate enhancement reaction                                         →
                                                                           D + NOx • ⎯⎯ D • + HNOx
                                                                                      kh 3



                         Termination by combination                                            →
                                                                              Rr • + Rs • ⎯⎯ Pr + s
                                                                                           ktc




                         Termination by disproportionation                                   →
                                                                            Rr • + Rs • ⎯⎯ Pr + Ps
                                                                                         ktd




                                                                            Rr • + M ⎯⎯→ Pr + M •
                                                                                            k
                         Transfer to monomer                                          fM



                                                                                                        37
                                                                            Rr • + D ⎯⎯→ Pr + D •
                                                                                            k
                         Transfer to dimer                                            fD
                                                Description                                 Step

                         Chemical initiation                                       →
                                                                            I ⎯ k⎯ 2 Rin •
                                                                                 d




                         Nitroxyl ether decomposition                              ⎯⎯⎯
                                                                                    ka 2
                                                                                         →
                                                                            NOE ←⎯⎯ Rin • + NO x •
                                                                                 kd 2



                         Mayo dimerization                                  M + M ⎯ k⎯ → D
                                                                                     d im
(Bonilla et al., 2002)
Kinetic Mechanism


                         Thermal initiation                                             →
                                                                            M + D ⎯⎯ D •+M •
                                                                                   ki a




                                                          07
                                                                                         →
                                                                            Rin • + M ⎯⎯ R1 •
                                                                                            k
                         First propagation (primary radicals)                          p




                                                                                       →
                                                                            M • + M ⎯⎯ R1 •
                                                                                        k
                         First propagation (monomeric radicals)                      p




                                                                                       →
                                                                            D • + M ⎯⎯ R1 •
                                                                                        k




                                              20
                         First propagation (dimeric radicals)                        p




                                                                                           →
                                                                             R r • + M ⎯ ⎯ R r +1 •
                                                                                                k
                         Propagation                                                     p




                         Dormant living exchange (monomeric alkoxyamine)                        ←⎯⎯
                                                                                                 ka


                              R                                                               →
                                                                            M • + NOx • ⎯⎯ MNOx
                                                                                         k da



                         Dormant living exchange (polymeric alkoxyamine)                        ←⎯⎯
                                                                                                  a k

                                                                                              →
                                                                            Rr • + NOx • ⎯⎯ Rr NOx
                                                                                          kda
                         IP
                                                                                        →
                                                                           MNOx ⎯⎯⎯ M + HNOx
                                                                                    k
                         Alkoxyamine decomposition                               decomp




                         Rate enhancement reaction                                         →
                                                                           D + NOx • ⎯⎯ D • + HNOx
                                                                                      kh 3



                         Termination by combination                                            →
                                                                              Rr • + Rs • ⎯⎯ Pr + s
                                                                                           ktc




                         Termination by disproportionation                                   →
                                                                            Rr • + Rs • ⎯⎯ Pr + Ps
                                                                                         ktd




                                                                            Rr • + M ⎯⎯→ Pr + M •
                                                                                            k
                         Transfer to monomer                                          fM



                                                                                                        38
                                                                            Rr • + D ⎯⎯→ Pr + D •
                                                                                            k
                         Transfer to dimer                                            fD
Thermal Self initiation of Styrene




                     07
                20
            R
         IP


                                     39
     IP
       R
           20
                07
40

				
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