Transcript OC 2/e 12 - Willson Research Group Home Page

Macromolecular Chemistry
N
N
N
Cu
+
N
BR-
Lecture 7
Chemistry 367L/392N
Decomposition of Thermal Initiator
kd
→ 2 R·
I
Efficiency factor ( f ):
CN
O
O
O
N
N
O
CN
di-tert-butylperoxide
f = 0.65
Ri =
dt
O
O
O
AIBN
f = 0.75
d [ R •]
O
di-tert-butylperoxalate
f=0.95
= 2 f k [ I]
d
Chemistry 367L/392N
Kinetics of free radical polymerization
 Steady state assumption:
Ri = Rt
- d[M·]
Ri=
= 2 kt [M·]2 Where kt = ktc+ ktd
dt
fk d [ I ]
2 fk [ I ] = 2 k [ M ] 2
So…
d
[M·]=
t
kt
What is the Propagation rate ( Rp )
-d[M]
= kp[M][M·]
Rp=
dt
-d[M]
= kp[M]
Rp=
dt
fkd[ I ]
kt
Chemistry 367L/392N
Kinetics of free radical polymerization
Average kinetic chain length ( Ӯ )
Rp Rp
=
Ӯ =
Ri Rt
k p [M ]
k p[M ]
[ M ][ M ]
=
=2
Ӯ=Kp
2
2 kt [ M ]
2kt [ M ]
( fktkd[ I ]
Disproportionation : DP = Ӯ
Combination :
DP = 2Ӯ
Chemistry 367L/392N
The chain growth system
The relationship between DP and conversion
With termination reactions
Chemistry 367L/392N
TEMPO 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
O
+
O
N
N
(2,2,6,6-tetramethylpiperidinyl-1-oxy)
TEMPO
Monomer
Polymer
Polymer
+
O
O
N
N
DP =
[monomer]
[Initiator]
Chemistry 367L/392N
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
100
50
conversion
Chain polymerization without termination
e.g. nitroxide-mediated radical polymerization
DP =
“Living”
[monomer]
[Initiator]
DP
Initiator decomposes quickly (high temp)
polymer chains have long life times
Chemistry
100
50
conversion
367L/392N
Controlled Free Radical Polymerization
Chemistry 367L/392N
Library of alkoxyaminesevaluated as initiators for the living
free radical polymerization of styrene and n-butyl acrylate.
Chemistry 367L/392N
Acrylates???
TEMPO
Chemistry 367L/392N
Published Example of Block Copolymer Formation
n-1
Ph
Ph
m
AIBN, heat
O
OMe
D : n = 60
: m = 20
N
SG1
Ph
n
n = 60
P
OEt
O OEt
O
n-1
Ph
Ph
heat
Reversible trapping prevents
irreversible termination
Ph
n-1
Ph
+
N
O
SG1
OMe
A living poly(styrene) block heated
in the presence of methyl acrylate
to give diblock D
OEt
P
OEt
O
m
O
n-1
Ph
Ph
propagation
m = 20
O N
m
O
O
P
O
O
OMe
D : n = 60
: m = 20
Chemistry 367L/392N
Control of polymer Architecture
O
O
O
N
O
+
O
CH3
AIBN
O
O
O
O
OCH3
OTEMPO
O
OCH3
O
OCH3
O
OTEMPO
Chemistry 367L/392N
O
O
O
OCH3
O
O
OCH3
O
OCH3
O
OTEMPO
OTEMPO
O
O
O
O
OCH3
O
OCH3
O
OCH3
O
Ph
Ph
Ph
Ph
Chemistry 367L/392N
Step growth system
The relationship between Mwt and conversion
Chemistry 367L/392N
The chain growth system
The relationship between Mwt and conversion
With termination reactions
Chemistry 367L/392N
The chain growth system
The relationship between Mwt and conversion
With no termination reactions
Chemistry 367L/392N
Other Controlled/Living Radical Polymerizations
Nitroxide mediated
stable free radicals e.g. TEMPO
Atom Transfer Polymerisation
Cu(I)Br/Ligand
RAFT
thioesters/xanthates
Chemistry 367L/392N
Atom Transfer Radical Polymerization - ATRP
R
X + Metal (n)
R
+ Metal (n + 1)
Br
+
CuBr
+
CuBr2
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
Chemistry 367L/392N
ATRP
N
N
N
Cu
+
N
BR-
ATRP works on Acrylates !!
Macromolecules, 30 (25), 7697 -7700, 1997
.
Chemistry 367L/392N
Living Free-Radical Polymerization by Reversible
Addition-Fragmentation Chain Transfer: The RAFT Process
Magic Reagent
Macromolecules, 31 (16), 5559 -5562, 1998
Chemistry 367L/392N
Radical addition to Dithionate esters
R''
R''
S
R'
S
S
R
R'
S
R
A Dithionate
R''
S
R'
S
+
R
Chemistry 367L/392N
RAFT Polymerisation
S
CH 3
S
I
C
n-1
O
O
.
S
n
Kadd
O
CH 3
CH 3
CH 3
I
O
O
O
CH 3
CH 3
S
CH 3
O
O
K-add
CH 3
RAFT polymerisation of
MMA with 2-phenylprop-2-yl
dithiobenzoate (1).
KP
I
(1)
K
.
S
S
I
n
O
O
O
H 3C
CH 3
O
m
H 3C
O
O
CH 3
C
O
O
CH 3
CH 3
CH 3
KP
CH 3
C
Chemistry 367L/392N
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
Chemistry 367L/392N
CRP - Issues
• Colored Products
• Strange Chain ends
• Metal Contamination
• The role of Cu in ATRP
• Sociology and psychology
FRONTIERS IN POLYMER CHEMISTRY
VIRGIL PERCEC, GUEST EDITOR
Chemical Reviews
Volume 101, Issue 12 (December 12, 2001)
Chemistry 367L/392N
Measuring Molecular Weight




 Alfredo
Vapor Phase Osmometry  Linda
Membrane Osmometry
Viscometry
Gel Permeation Chromatography
– Size exclusion Chromatography



Light Scattering
MALDI
Others
– End group analysis
 , etc.
Chemistry 367L/392N
Definition of viscosity:
For normal (Newtonian) flow behaviour:
viscosity
t = (F/A) = h . (dv/dy)
shear
stress
shear rate
units: (dyne/cm2)/sec-1
h = t/(dv/dy)
.
= dyne.sec.cm-2.
= POISE (P)
At 20.0oC, h(water) ~ 0.01P = 1.0 Centipoise
Chemistry 367L/392N
Viscosity of Polymer solutions:
A dissolved macromolecule will INCREASE the
viscosity of a solution because it disrupts the
streamlines of the flow:
Chemistry 367L/392N
Ubbelohde Viscometer
Chemistry 367L/392N
Types of Viscometers:
1.
2.
“U-tube” (Ostwald or
Ubbelohde)
“Cone & Plate”
(Couette)
Chemistry 367L/392N
Relative viscosity hr
We define the relative viscosity hr 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/ho
units?
For a U-tube viscometer, hr = (t/to). (r/ro)
Chemistry 367L/392N
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
Chemistry 367L/392N
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] = Limc 0 (hred)
⃗
units [h] = ?
Chemistry 367L/392N
Molecular Weight from [h]
Mark-Houwink-Kuhn-Sakurada equation
[h] = K’ Ma
a=0
a = 0.5-0.8
a = 1.8
Chemistry 367L/392N
Representative Viscosity-Molecular Weight Constantsa
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)
30-70 mol%
71-29 mol%
Poly(ethylene terephthalate)
Nylon 66
aValue
Solvent
Temp oC Molecular Weight b
K  103
-4
Range  10
Cyclohexane
Cyclihexane
Benzene
Decalin
35 d
50
25
135
8-42e
4-137e
3-61f
3-100e
Benzyl alcohol
Cyclohexanone
155.4d
20
4-35e
7-13f
156
13.7
0.50
1.0
Toluene
Toluene
DMFg
DMF
30
30
25
25
5-50f
5-16f
5-27e
3-100f
30.5
29.4
16.6
39.2
0.725
0.753
0.81
0.75
30
30
25
25
5-55e
1-Chlorobutane
1-Chlorobutane
M-Cresol
M-Cresol
0.50
0.599
0.74
0.67
80
26.9
9.52
67.7
17.6
24.9
0.77
240
4.18-81e
0.04-1.2f
1.4-5f
taken from Ref. 4e. bSee text for explanation of these constants.
average. fNumber average. gN,N-dimethylformamide.
ab
cAtactic
d
temperature.
0.67
0.63
0.95
0.61
Weight
Chemistry 367L/392N