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

Investigating Nitroxide-Mediated Radical Polymerization of Styrene over a Range of Reaction Conditions A. Nabifar N. T. McManus A. Penlidis Institute for Polymer Research (IPR) Department of Chemical Engineering University of Waterloo 1

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) 2

Controlled Radical Polymerization (CRP) Regular Radical Polymerization Controlled Radical Polymerization Living Ionic Polymerization 3

Controlled Radical Polymerization (CRP) Examples of molecular structures attained 4

Controlled Radical Polymerization (CRP) Applications Acrylic block copolymers as stabilizers in coating, ink applications Additives suitable for use as components of lubricating oils ABC type block copolymers 5

Controlled Radical Polymerization (CRP) Nitroxide- Mediated Radical Polymerization (NMRP) R Atom Transfer Radical Polymerization (ATRP) R Br + CuBr (L) R Reversible Addition-Fragmentation Transfer (RAFT) R m S C S TEMP K a K d K a K d R + TEMP + CuBr 2 (L) + + R R S C S R n K exch m n z z 6

Controlled Radical Polymerization (CRP) R + X R X (Active) K deact K act (Dormant) Exchange equilibrium favours dormant species Concentration of radicals is low; bimolecular termination almost negligible Radicals grow at the same average rate; low polydispersity product 7

Controlled Radical Polymerization (CRP) 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) 8

Controlled Radical Polymerization (CRP) ln([m]0/[m]) slow initiation living state termination M n time FRP LRP conversion Deviation from linearity can result from slow initiation or loss of radicals by termination 9

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 TEMP (2, 2, 6, 6 tetramethyl-1-piperidinyloxy) 10

NMRP of Styrene with BP and TEMP + STY Initiator efficiency factor (f) k i Initiation (Thermal) Self initiation of Styrene Benzoyl Peroxide Benzoyloxy radical 2 C 11

NMRP of Styrene with BP and TEMP C n + n C + N TEMP k p Propagation k deact k act x n C N K = k deact / k act 12

Side Reactions Reaction between TEMP and BP N C Nitroxide decomposition C N + 13

Uncertain Aspects (?) Initiator efficiency factor (f) Uncertain kinetic constants Side reactions 14

bjectives Clarify the effect of polymerization conditions (TEMP/ BP 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 15

Summary of Runs Temperature ( C) 120 130 [BP] 0 M 0.036 0.036 0.036 0.036 Nil 0.036 0.036 0.036 Nil Nil [TEMP] / [BP] 0.9 1.1 + Replicate 1.2 1.5-0.9 1.1 1.3 - Remarks Styrene with unimolecular initiator + Replicate + Replicate Thermal (self) initiation of styrene + Replicate - Styrene with TEMP only 16

Effect of TEMP/BP Ratio Conversion, X 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 TEMP/BP=0.9 TEMP/BP = 1.1 TEMP/BP=1.1,Independent replicate TEMP/BP = 1.2 TEMP/BP = 1.5 0 10 20 30 40 50 60 70 80 Time, t (hr) STY polymerization at 120 C, [BP] 0 = 0.036 M 17

Weight Average Molecular Weight (gr/mol) 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 0 0.2 0.4 0.6 0.8 1 Conversion, X TEMP/BP=0.9 TEMP/BP=1.1 TEMP/BP=1.2 TEMP/BP=1.5 STY polymerization at 120º C, [BP] 0 = 0.036 M 18

Polydispersity, PDI 9 8 7 6 5 4 3 2 1 0 TEMP/BP=0.9 TEMP/BP=1.1 TEMP/BP=1.2 TEMP/BP=1.5 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, [BP] 0 = 0.036 M 19

bservations The larger the TEMP/ BP ratio (the more TEMP in the recipe), the slower the polymerization Higher values of average molecular weights, Mn and Mw, are obtained as TEMP/BP ratio decreases Low PDI values, below 1.2 Similar trends with experimental data at 130 C (not shown) 20

Effect of Temperature Conversion, X 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 130 120 0 10 20 30 40 50 60 70 80 Time, t (hr) STY polymerization at TEMP / BP = 0.9 21

Weight Average Molecular Weight (gr/mol) PDI 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 1.8 1.6 1.4 1.2 1 T = 130 T = 120 T = 120,Independent replicate 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 TEMP / BP = 0.9 22

Mathematical Modeling Kinetic model based on a detailed reaction mechanism Molar balances; population balances; set of ordinary differential equations General trends K Satisfactory prediction of experimental data but more work needs to be done ( fine-tuning of key but uncertain parameters) 23

Concluding Remarks ptimal ratio to achieve lowest polydispersity seems to be around [TEMP]/ [BP] = 1.2 There is no pronounced temperature effect at studied conditions Model trends and preliminary predictions satisfactory for typical polymerization variables (on going work) PDI 1.5 1.4 1.3 1.2 1.1 1 0.9 1.1 1.2 1.5 TEMP/BP Ratio 24

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 mechanism 25

Acknowledgements NSERC CR Grant GSST MNVA Solutions Canada Research Chair (CRC) program ( A. Penlidis) CR 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 ) 26

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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., dell, 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. 28

CH 2 CH CH 2 CH n N k decomp CH 2 CH CH CH H N n + 29

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) 30

Conversion, X Results 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Replicate 0 10 20 30 40 50 60 Time, t (hr) Ln [M]0/[M] 2.5 2 1.5 1 0.5 0 0 5 10 15 20 25 30 35 Time, t (hr) STY polymerization at 120 C, TEMP/BP = 1.1 31

Average Molecular Weights (gr/mol) PDI 30,000 25,000 20,000 15,000 10,000 5,000 0 1.6 1.4 1.2 1 Mn Mw 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, TEMP/BP = 1.1 32

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 TEMP/ BP=1.1 33

Mathematical Modeling 1 Conversion, X 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 Experimental data 0.1 Predicted Profile 0 0 5 10 15 20 25 30 35 40 Time, t (hr) Number Average Molecular Weight (g/mol) 35000 30000 25000 20000 15000 10000 5000 Experimental data Predicted Profile 0 0.0 0.2 0.4 0.6 0.8 1.0 Conversion, X STY polymerization at T = 130 C,TEMP/BP = 1.1 34

PDI 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 Predicted Experimental data Profile 0 0.2 0.4 0.6 0.8 1 Conversion, X STY polymerization at T = 130 C,TEMP/BP = 1.1 35

0.024 Concentration, mol/l 0.022 0.02 0.018 0.016 0.014 0.012 0.01 0.008 0.006 0.004 [I] [Nx*] 0.002 [Ne] 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 d 2R in 2 Nitroxyl ether decomposition k a N R + N E k in x d 2 Kinetic Mechanism (Bonilla et al., 2002) Mayo dimerization Thermal initiation First propagation (primary radicals) k dim M + M D M D D M i + k a + k p R + M R First propagation (monomeric radicals) k M + M p R1 First propagation (dimeric radicals) k D + M p R1 Propagation Dormant living exchange (monomeric alkoxyamine) Dormant living exchange (polymeric alkoxyamine) in r k p R + M R + 1 1 k a M + N MN x kda k a R + N R N r x k r x da k Alkoxyamine decomposition MN decomp M + HN Rate enhancement reaction 3 D+ N k h D + HN Termination by combination x x R + R P + k tc r s r s r x x x Termination by disproportionation Transfer to monomer Transfer to dimer R + R P + P r k td r s r s k fm R + M P + M r k fd R + D P + D r r 37

Description Step Chemical initiation I k d 2R in 2 Nitroxyl ether decomposition k a N R + N E k in x d 2 Kinetic Mechanism (Bonilla et al., 2002) Mayo dimerization Thermal initiation First propagation (primary radicals) k dim M + M D M D D M i + k a + k p R + M R First propagation (monomeric radicals) k M + M p R1 First propagation (dimeric radicals) k D + M p R1 Propagation Dormant living exchange (monomeric alkoxyamine) Dormant living exchange (polymeric alkoxyamine) in r k p R + M R + 1 1 k a M + N MN x kda k a R + N R N r x k r x da k Alkoxyamine decomposition MN decomp M + HN Rate enhancement reaction 3 D+ N k h D + HN Termination by combination x x R + R P + k tc r s r s r x x x Termination by disproportionation Transfer to monomer Transfer to dimer R + R P + P r k td r s r s k fm R + M P + M r k fd R + D P + D r r 38

Thermal Self initiation of Styrene 39

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