Lecture 12 - University of Texas at Austinwillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture...
Transcript of Lecture 12 - University of Texas at Austinwillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture...
Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 12 Lecture 12
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Chemistry 367L/392N
Chain Transfer in Free Radical Chain Transfer in Free Radical PolymerizationPolymerization
� A termination and re-initiation reaction
� For Chain Transfer Y• must be able to re-initiate reaction
Chemistry 367L/392N
Chain Transfer Agents (Chain Transfer Agents (CTAsCTAs))
� Thiols are efficient examples
Chemistry 367L/392N
DPDPnn = degree of = degree of polymerisationpolymerisationWITH transfer agentWITH transfer agent
DPDPoo = degree of = degree of polymerisationpolymerisationWITHOUT transfer agentWITHOUT transfer agent
Measurement of Chain Transfer ConstantsMeasurement of Chain Transfer Constants
+=monomer
gentTransfer aCs
DPDPn 0
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CCSS = Chain Transfer = Chain Transfer ““ constantconstant”” or or ““ coefficientcoefficient””
The Mayo Equation:The Mayo Equation:
Chemistry 367L/392N
1/DP0
Cs
1/D
P
[S]/[M]
Generic Mayo plot
Chemistry 367L/392N
BButylatedutylated HHydroxyydroxyTTolueneoluene� BHT radical will not initiate new chains� So…BHT is an inhibitor, not a CTA
Chemistry 367L/392N
Interesting Interesting ““InhibitorsInhibitors”…”…..
N
O
N
O
PhenylPhenyl--aa--tt--butylnitronebutylnitrone
PBNPBN
TEMPOTEMPO
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
Free Radical CopolymerizationFree Radical Copolymerization
What happens when we initiate a polymerization in a mixture of monmers???
Random Copolymers Random Copolymers MM11MM22MM11MM11MM22MM22MM22MM11MM11MM22
Block Copolymers Block Copolymers MM11MM11MM11MM11MM22MM22MM22MM22MM22MM22
Alternating Copolymers Alternating Copolymers MM11MM22MM11MM22MM11MM22MM11MM22MM11MM22
MM11 +M+M22 →→ --[([(MM11))xx--(M(M22))yy]]nn--AIBNAIBN
Chemistry 367L/392N
Free Radical CopolymerizationFree Radical Copolymerization
~
~
~
~
~
~
~
~
Assume chain end concentrations are constant at “st eady state”
Free Radical Co-polymerization
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a
b
pages 467-469 !!
Do the algebra -see
is a/b
Chemistry 367L/392N
If r1 > 1 means M
If r 1 >1 this means that ~M 1• adds M 1 more readily than M 2. If r 1 is zero then M 1 does not undergo homopolymerization!!
This important relationship can be expressed in This important relationship can be expressed in terms of mole fractions rather than concentrationsterms of mole fractions rather than concentrations
Chemistry 367L/392N
This gives the Instantaneous mole fraction of M 1 in the copolymer
Supplementary Homework!
Chemistry 367L/392N
How does one determine the reactivity rations??
•Fineman Method
•Kelen-Tudos Method
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.00.0
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A = styreneB = butadienera = 0.75, rb = 1.3
F
a (p
olym
er c
ompo
sitio
n)
fa (monomer composition)
Ideal copolymer
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.00.0
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A = styreneB = maleic anhydridera = 0.05, rb = 0.0
F
a (p
olym
er c
ompo
sitio
n)
fa (monomer composition)
Alternating Copolymer
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.00.0
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A = vinyl acetateB = styrenera = 0.01, rb = 50
F
a (c
ompo
sitio
n of
pol
ymer
)
fa (Composition of monomer)
Rich in one monomer
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.00.0
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A = AcrylonitrileB = Butadienera = 0.046, rb = 0.36
F
a (p
olym
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ompo
sitio
n)
fa (monomer composition)
Quite typical copolymerisation