Macromolecular Chemistry

Transcription

1 Macromolecular Chemistry N N N Cu + BR - N Lecture 7

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

3 R i = Kinetics of free radical polymerization Ri = Rt - d[m ] dt Steady state assumption: = 2 k t [M ] 2 Where k t = k tc + k td 2 fk [ I ] = 2k [ M d t What is the Propagation rate ( Rp ) ] 2 So [M ]= fk d[ I ] fk k t R p = -d[m] = kp [M][M ] dt R p = -d[m] = kp [M] dt fk d[ I] fk k t

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

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

6 TEMP Controlled Polymerization 1993 M. K. Georges, R. P. N. Veregin,, P. M. Kazmaier and G. K. Hamer (Xerox Corporation), "Narrow Molecular Weight Resin by Free Radical Process." I I N + N (2,2,6,6-tetramethylpiperidinyl-1-oxy) TEMP Monomer Polymer + N Polymer N DP = [monomer] [Initiator]

7 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 DP conversion Chain polymerization without termination e.g. nitroxide-mediated radical polymerization DP = [monomer] [Initiator] DP Living Initiator decomposes quickly (high temp) polymer chains have long life times conversion

8 Controlled Free Radical Polymerization

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

10 Acrylates??? TEMP

11 Published Example of Block Copolymer Formation n-1 m Ph Ph Me D : n = 60 : m = 20 Ph n AIBN, heat SG1 n = 60 Ph N n-1 Ph P Et Et heat Reversible trapping prevents irreversible termination Ph n-1 Ph + N SG1 P Et Et A living poly(styrene) block heated in the presence of methyl acrylate to give diblock D Ph Me m N n-1 m Ph Me D : n = 60 : m = 20 propagation m = 20 P

12 Control of polymer Architecture N + CH 3 AIBN CH 3 CH 3 CH 3 TEMP TEMP

13 CH 3 CH 3 CH 3 TEMP TEMP CH 3 CH 3 CH 3 Ph Ph Ph Ph

14 Step growth system The relationship between M wt and conversion

15 The chain growth system The relationship between M wt and conversion With termination reactions

16 The chain growth system The relationship between M wt and conversion With no termination reactions

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

18 Atom Transfer Radical Polymerization - ATRP R X + Metal (n) R + Metal (n + 1) Br + CuBr + CuBr 2 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

19 ATRP N N N Cu + BR - N ATRP works on Acrylates!! Macromolecules, 30 (25), , 1997.

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

21 Radical addition to Dithionate esters R'' S R R' S A Dithionate R'' R' S S R R'' R' S + R S

22 RAFT Polymerisation I S S CH 3 CH CH 3 3 (1) n-1 C S. S I n CH K 3 add CH CH 3 3 K -add CH 3 CH 3 H 3 C C H 3 I. K P CH 3 RAFT polymerisation of MMA with 2-phenylprop-2-yl dithiobenzoate (1). m C CH 3 CH 3 K P I n CH 3 S K β CH 3 C CH 3 S

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

24 CRP - Issues Colored Products Strange Chain ends Metal Contamination The role of Cu in ATRP Sociology and psychology FRNTIERS IN PLYMER CHEMISTRY VIRGIL PERCEC, GUEST EDITR Chemical Reviews Volume 101, Issue 12 (December 12, 2001)

25 Measuring Molecular Weight Membrane smometry Alfredo Vapor Phase smometry Linda Viscometry Gel Permeation Chromatography Size exclusion Chromatography Light Scattering MALDI thers End group analysis, etc.

26 Definition of viscosity: For normal (Newtonian) flow behaviour: τ = (F/A) = η. (dv/dy) shear stress viscosity η = τ/(dv/dy) shear rate units: (dyne/cm 2 )/sec -1 = dyne.sec.cm -2.. = PISE (P) At 20.0 o C, η(water) ~ 0.01P = 1.0 Centipoise

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

28 Ubbelohde Viscometer

29 Types of Viscometers: 1. U-tube (stwald or Ubbelohde) 2. Cone & Plate (Couette)

30 Relative viscosity η r We define the relative viscosity η r as the ratio of the viscosity of the solution containing the macromolecule, η, to that of the pure solvent in the absence of macromolecule, η o : η r = η/η o units? For a U-tube viscometer, η r = (t/t o ). (ρ/ρ o )

31 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 η red red = (η r 1)/c Reduced viscosity Where C is the concentration in gm/ml

32 The Intrinsic Viscosity [η][ To eliminate non-ideality effects deriving from exclusion volume, backflow and charge effects, etc we by analogy with osmotic pressure, measure η red at a series of concentrations and extrapolate to zero concentration: [η] ] = Lim c 0 (η red ) units [η] =?

33 Molecular Weight from [η][ Mark-Houwink-Kuhn-Sakurada equation [η]] = K K M a a = 0 a = a = 1.8

34 Representative Viscosity-Molecular Weight Constants a 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-costyrene) mol% mol% Poly(ethylene terephthalate) Nylon 66 Solvent Cyclohexane Cyclihexane Benzene Decalin Benzyl alcohol Cyclohexanone Toluene Toluene DMF g DMF 1-Chlorobutane 1-Chlorobutane M-Cresol M-Cresol Temp o C 35 d d Molecular Weight Range e e 3-61 f e 4-35 e 7-13 f 5-50 f 5-16 f 5-27 e f 5-55 e e f f K b a b a Value taken from Ref. 4e. b See text for explanation of these constants. c Atactic average. f Number average. g N,N-dimethylformamide. d θ temperature. Weight