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Macromolecular Chemistry

Macromolecular Chemistry. Lecture 7. k. d. [. ]. d. R. •. [. ]. =. =. I. R. 2. f. k. dt. i. d. Decomposition of Thermal Initiator. I → 2 R·. Efficiency factor ( f ):. di- tert -butylperoxide AIBN di- tert -butylperoxalate f = 0.65 f = 0.75 f=0.95.

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Macromolecular Chemistry

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  1. Macromolecular Chemistry Lecture 7

  2. k d [ ] d R • [ ] = = I R 2 f k dt i d Decomposition of Thermal Initiator I → 2 R· Efficiency factor ( f ): di-tert-butylperoxide AIBN di-tert-butylperoxalate f = 0.65 f = 0.75 f=0.95

  3. Where kt = ktc+ ktd Ri= =2 kt [M·]2 dt -d[M] = kp[M][M·] Rp= dt fk fk [ [ I I ] ] d d k k t t Kinetics of free radical polymerization Ri = Rt  Steady state assumption: -d[M·] = × 2 fk [ I ] 2 k [ M ] 2 So… [M·]= d t What is the Propagation rate ( Rp ) -d[M] = kp[M] Rp= dt

  4. Kinetics of free radical polymerization Average kinetic chain length(Ӯ) R R p p = = Ӯ R R i t k [ M ] k [ M ] × [ M ][ M ] p p Ӯ = = = 2 K p × 2 × 2 2 k [ M ] ( fk k [ I ] k [ M ] t d t t Ӯ  Disproportionation : Combination : DP = 2Ӯ DP =

  5. The chain growth system The relationship between DP and conversion With termination reactions

  6. I I O N O N + M o n o m e r P o l y m e r O N P o l y m e r O N + TEMPO Controlled Polymerization (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMPO

  7. DP 100 50 conversion “Living” DP 100 50 conversion Radical Chain Growth Chain polymerization with termination • Life time of polymer radical chain is about 1 second • Initiator slowly decomposes throughout polymerization time • Steady State approximation: • rate of initiation = rate of termination • Therefore, [propagating radical] remains constant Chain polymerization without termination e.g. nitroxide-mediated radical polymerization Initiator decomposes quickly (high temp) polymer chains have long life times

  8. Controlled Free Radical Polymerization

  9. Library of alkoxyaminesevaluated as initiators for the living free radical polymerization of styrene and n-butyl acrylate.

  10. Acrylates??? TEMPO

  11. Published Example of Block Copolymer Formation Reversible trapping prevents irreversible termination A living poly(styrene) block heated in the presence of methyl acrylate to give diblock D

  12. Control of polymer Architecture

  13. Step growth system The relationship between Mwt and conversion

  14. The chain growth system The relationship between Mwt and conversion With termination reactions

  15. The chain growth system The relationship between Mwt and conversion With no termination reactions

  16. Other Controlled/Living Radical Polymerizations Nitroxide mediated stable free radicals e.g. TEMPO Atom Transfer Polymerisation Cu(I)Br/Ligand RAFT thioesters/xanthates

  17. Atom Transfer Radical Polymerization - ATRP K. Matyjaszewski: Macromolecules 1997, 30, p7697; 7042; 7034; 7348; 8161; 7692; 6507, 6513, 6398 JACS 1997, 119, p674 V Percec: Macromolecules 1997, 30, p6705, 8526 M Sawamoto: Macromolecules 1997, 30, p2244, 2249 Teyssie: Macromolecules 1997, 30, p7631, Haddleton: Macromolecules 1997, 30, p2190

  18. ATRP ATRP works on Acrylates !! Macromolecules, 30 (25), 7697 -7700, 1997.

  19. Living Free-Radical Polymerization by Reversible Addition-Fragmentation Chain Transfer: The RAFT Process Magic Reagent Macromolecules, 31 (16), 5559 -5562, 1998

  20. Radical addition to Dithionate esters

  21. RAFT Polymerisation

  22. RAFT works!! Molecular weight distributions for poly(styrene-co-acrylonitrile) polymerized by heating styrene and acrylonitrile (62:38 mole ratio) at 100 C in the presence of cumyl dithiobenzoate

  23. CRP - Issues • Colored Products • Strange Chain ends • Metal Contamination • The role of Cu in ATRP • Sociology and psychology FRONTIERS IN POLYMER CHEMISTRYVIRGIL PERCEC, GUEST EDITOR Chemical Reviews Volume 101, Issue 12 (December 12, 2001)

  24. Measuring Molecular Weight • Membrane Osmometry  Alfredo • Vapor Phase Osmometry  Linda • Viscometry • Gel Permeation Chromatography • Size exclusion Chromatography • Light Scattering • MALDI • Others • End group analysis  , etc.

  25. Definition of viscosity: For normal (Newtonian) flow behaviour: t = (F/A) = h . (dv/dy) viscosity shear rate units: (dyne/cm2)/sec-1 = dyne.sec.cm-2. . = POISE (P) shear stress h = t/(dv/dy) At 20.0oC, h(water) ~ 0.01P = 1.0 Centipoise

  26. Viscosity of Polymer solutions: A dissolved macromolecule will INCREASE the viscosity of a solution because it disrupts the streamlines of the flow:

  27. Ubbelohde Viscometer

  28. Types of Viscometers: • “U-tube” (Ostwald or Ubbelohde) • “Cone & Plate” (Couette)

  29. Relative viscosity hr We define the relative viscosityhr as the ratio of the viscosity of the solution containing the macromolecule, h, to that of the pure solvent in the absence of macromolecule, ho: hr = h/hounits? For a U-tube viscometer, hr = (t/to). (r/ro)

  30. Reduced viscosity The relative viscosity depends (at a given temp.) on the concentration of macromolecules, the shape of the macromolecule & the volume it occupies. We can infer things about the shape and volume of the macromolecule if we eliminate the concentration contribution. The first step is to define the reduced viscosity hred = (hr– 1)/c Where C is the concentration in gm/ml

  31. The Intrinsic Viscosity [h] To eliminate non-ideality effects deriving from exclusion volume, backflow and charge effects, etc we by analogy with osmotic pressure, measure hred at a series of concentrations and extrapolate to zero concentration: [h] = Limc⃗0(hred) units [h] = ?

  32. Molecular Weight from [h] Mark-Houwink-Kuhn-Sakurada equation [h] = K’ Ma a = 0 a = 0.5-0.8 a = 1.8

  33. Temp oC 35 d 50 25 135 155.4d 20 30 30 25 25 30 30 25 25 Molecular Weight Range  10-4 8-42e 4-137e 3-61f 3-100e 4-35e 7-13f 5-50f 5-16f 5-27e 3-100f 5-55e 4.18-81e 0.04-1.2f 1.4-5f ab 0.50 0.599 0.74 0.67 0.50 1.0 0.725 0.753 0.81 0.75 0.67 0.63 0.95 0.61 Solvent Cyclohexane Cyclihexane Benzene Decalin Benzyl alcohol Cyclohexanone Toluene Toluene DMFg DMF 1-Chlorobutane 1-Chlorobutane M-Cresol M-Cresol Polymer Polystyrene (atactic)c Polyethylene (low pressure) Poly(vinyl chloride) Polybutadiene 98% cis-1,4, 2% 1,2 97% trans-1,4, 3% 1,2 Polyacrylonitrile Poly(methyl methacrylate-co-styrene) 30-70 mol% 71-29 mol% Poly(ethylene terephthalate) Nylon 66 Kb 103 80 26.9 9.52 67.7 156 13.7 30.5 29.4 16.6 39.2 17.6 24.9 0.77 240 Representative Viscosity-Molecular Weight Constantsa aValue taken from Ref. 4e. bSee text for explanation of these constants. cAtactic d temperature. Weight average. fNumber average. gN,N-dimethylformamide.

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