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Free Radical Polymerizations

Free Radical Polymerizations. Reading assignments: Chapter 3-3, 3-4, 3-5, 3-8 (Odian). Free Radical Solution Polymerizations. Initiation Propagation Termination. d [ R • ] / dt = 2 k d [ I ]. = 2 f k d [ I ]. - d [ R • ] / dt = k i [R•] [M]. r p = k p [ M •] [M].

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Free Radical Polymerizations

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  1. Free Radical Polymerizations

  2. Reading assignments: Chapter 3-3, 3-4, 3-5, 3-8 (Odian)

  3. Free Radical Solution Polymerizations • Initiation • Propagation • Termination d [R•] / dt = 2 kd[I] = 2 fkd[I] - d [R•] / dt = ki[R•][M] rp = kp[M•][M] - d [P•] / dt = 2 kt[P•]2

  4. Free Radical Solution Polymerizations • Overall rate expression • Assumptions? • Steady State Approximation (Ri = Rt) Rp = kp[M][M•] 2 fkd [I]= 2 kt[M•]2 [M•]= (kd f [I] / kt)1/2 Rp = kp[M] (kd f[I]/ kt)1/2

  5. Free Radical Solution Polymerizations • Overall rate expression • Rate is first order in monomer • Rate is ½ order in initiator • To increase Rp Rp = kp[M] (kd f[I]/ kt)1/2

  6. Determination of Orders of Reaction  Rp  kp [Iout-I*] 0.5 [VF2]out1.0 T =75 °C, P= 4000 psig, CO2 = 0.74 g/ml Rp = ([VF2]IN-[VF2]OUT)/ [DEPDC]IN =3 mM Rp (mol/L x sec) Rp/[VF2]out (1/ sec) I* [VF2]out (mol/L) [I]out 0.5 (mol/L)

  7. Experimental Ways of Determining Rp • Separation and isolation of product • Precipitation • Chromatography • Chemical analysis • Titration of un-reacted double bonds… • Spectroscopic methods • UV/Vis, NMR, FTIR • Refractive index changes • Dilatometry • Calorimetry

  8. React-IR t = 30 s, 32 scans reaction conditions: p = 5000 p.s.i., T = 35 °C, 73 mol-% PDD in feed phase separation  emulsion

  9. Dilatometer

  10. Free Radical Solution Polymerizations • Overall rate expression • Rate is first order in monomer • Rate is ½ order in initiator • Qualitative picture…? Rp = kp[M] (kd f[I]/ kt)1/2

  11. Free Radical Solution Polymerizations Rp Rp ٧ = — = — Ri Rt kp [M][M•] kp [M] kp [M] ٧ = ———— = ——— = ————— 2 (ktkd f [I])1/2 2 kt [M•]2 2 kt [M•] • Kinetic Chain Length (٧) • Average number of monomer units polymerized per chain initiated

  12. Free Radical Solution Polymerizations kp [M] = ————— 2 (ktkd f [I])1/2 • Kinetic Chain Length (٧) • To increase molecular weight… • To increase Rate of Polymerization ٧ =

  13. Kinetic Chain Length (٧) vsDegree of Polymerization (DP) DP = 2٧ DP = ٧ • Termination by combination • Termination by disproportionation

  14. Classes of Free Radical Initiators

  15. Initiator Decompositions [I]0 [I]0 0.63 log —— = kdt t1/2 = ——— set: [I] = —— [I] kd 2 • Differences in the decomposition rates of various initiators can be expressed in terms of initiator half life • The rate of initiator disappearance is: • Integrate:or • Half life? - d[I] / dt = kd[I] [I] = [I]0e-kdt

  16. Factors which Influence Initiator Choice • Temperature of polymerization • Solubility of the initiator • End group control or functionalization

  17. Factors which Influence Initiator Choice • End group control or functionalization

  18. Pulsed-laser Polymerization in Homogeneous Phase: Determination of kp

  19. Pulsed-laser Polymerization in Homogeneous Phase: Determination of kp

  20. Evaluation of kp

  21. Kinetic Chain Length Profile in a PLP Experiment

  22. Li=i kp [M] td

  23. Li=i kp [M] td

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