Lecture 12
Lecture 12
Lecture 12
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Macromolecular Chemistry<br />
10<br />
5<br />
0.5<br />
0.1<br />
<strong>Lecture</strong> <strong>12</strong><br />
Chemistry 367L/392N
Chain Transfer in Free Radical<br />
Polymerization<br />
A termination and re-initiation reaction<br />
For Chain Transfer Y• must be able to re-initiate reaction<br />
Chemistry 367L/392N
Chain Transfer Agents (CTAs(<br />
CTAs)<br />
Thiols are efficient examples<br />
Chemistry 367L/392N
Measurement of Chain Transfer Constants<br />
The Mayo Equation:<br />
1 1<br />
=<br />
DP n DP 0<br />
⎡Transfer agent<br />
+ Cs⎢<br />
⎣ monomer<br />
⎤<br />
⎥<br />
⎦<br />
DP n<br />
DP o<br />
C S<br />
= degree of polymerisation WITH transfer agent<br />
= degree of polymerisation WITHOUT transfer agent<br />
= Chain Transfer “constant” or “coefficient”<br />
Chemistry 367L/392N
Generic Mayo plot<br />
1/DP<br />
Cs<br />
1/DP 0<br />
[S]/[M]<br />
Chemistry 367L/392N
Butylated<br />
HydroxyTolueneoluene<br />
<br />
<br />
BHT radical will not initiate new chains<br />
So…BHT is an inhibitor, not a CTA<br />
Chemistry 367L/392N
Interesting “Inhibitors”….<br />
N<br />
O<br />
Phenyl-a-t-butylnitrone<br />
PBN<br />
N<br />
O<br />
TEMPO<br />
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
Free Radical Copolymerization<br />
What happens when we initiate a<br />
polymerization in a mixture of monmers<br />
M 1 +M 2 → -[(M 1 ) x -(M<br />
2 ) y ] n -<br />
AIBN<br />
Random Copolymers M 1 M 2 M 1 M 1 M 2 M 2 M 2 M 1 M 1 M 2<br />
Block Copolymers M 1 M 1 M 1 M 1 M 2 M 2 M 2 M 2 M 2 M 2<br />
Alternating Copolymers M 1 M 2 M 1 M 2 M 1 M 2 M 1 M 2 M 1 M 2<br />
Chemistry 367L/392N
Free Radical Co-polymerization<br />
Free Radical Copolymerization<br />
~<br />
~<br />
~<br />
~<br />
~<br />
~<br />
~<br />
~<br />
Assume chain end concentrations are constant at “steady state”<br />
Chemistry 367L/392N
a<br />
b<br />
is a/b<br />
Do the algebra -see<br />
pages 467-469 !!<br />
Chemistry 367L/392N
If r<br />
If r1 > 1 >1 this means that ~M<br />
1<br />
1 • adds M 1 more readily<br />
than M<br />
means 2 . If r 1 is zero then M 1 does not undergo<br />
homopolymerization!!<br />
This important relationship can be expressed in<br />
terms of mole fractions rather than concentrations<br />
Chemistry 367L/392N
Supplementary<br />
Homework!<br />
This gives the Instantaneous mole<br />
fraction of M 1 in the copolymer<br />
Chemistry 367L/392N
How does one determine the<br />
reactivity rations<br />
•Fineman Method<br />
•Kelen-Tudos Method<br />
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
1.0<br />
Ideal copolymer<br />
Fa (polymer composition)<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
A = styrene<br />
B = butadiene<br />
ra = 0.75, rb = 1.3<br />
0.0<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
fa (monomer composition)<br />
Chemistry 367L/392N
Fa (polymer composition)<br />
1.0<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
Alternating Copolymer<br />
A = styrene<br />
B = maleic anhydride<br />
ra = 0.05, rb = 0.0<br />
0.0<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
fa (monomer composition)<br />
Chemistry 367L/392N
1.0<br />
Rich in one monomer<br />
Fa (composition of polymer)<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
A = vinyl acetate<br />
B = styrene<br />
ra = 0.01, rb = 50<br />
0.0<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
fa (Composition of monomer)<br />
Chemistry 367L/392N
1.0<br />
Quite typical copolymerisation<br />
Fa (polymer composition)<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
A = Acrylonitrile<br />
B = Butadiene<br />
ra = 0.046, rb = 0.36<br />
0.0<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
fa (monomer composition)<br />
Chemistry 367L/392N
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