Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture 13.pdf ·...
Transcript of Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture 13.pdf ·...
Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 13 Lecture 13
CH
R
H2C + CO CH2 CH
R
C
O
Chemistry 367L/392N
Free Radical CopolymerizationFree Radical Copolymerization
~
~
~
~
~
~
~
~
Assume chain end concentrations are constant at “steady state”
Free Radical Co-polymerization
Chemistry 367L/392N
If r1 > 1
means M
If r1 >1 this means that ~M1• adds M1 more readily than M2. If r1 is zero then M1 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
Copolymerization Equation
This gives the Instantaneous mole fraction of M1 in the copolymer
Chemistry 367L/392N
Finemann-Ross Equation
Finemann – Ross Equation
Chemistry 367L/392N
Chemistry 367L/392N
Let’s actually calculate r1 and r2 from some data
We run the copolymerization for a very short time starting with different weight ratios of 2 monomers.
The assumption is that f does not change in this
experiment
We isolate the small amount of polymer generated
and determine the ratio of monomers incorporated….by nmr, for example
We apply the Fineman-Ross analysis and extract
the reactivity ratios.
ChrisChris
Chemistry 367L/392N
Chemistry 367L/392N
r1 > 1, r2 < 1 or r1 < 1, r2 > 1
10
5
0.5
0.1
If r1 > 1 (k11 > k12) and r2 < 1 (k22 < k21) then M1 is more active than M2 whether either ~M1
• and ~M2•. F1 is
always larger than f1 and the curve is always above the diagonal.
The situation is similar for r1 < 1, r2 > 1 but the curve is below the diagonal.
Chemistry 367L/392N
as r1 x r2 = 1 (r2=1/r1), it becomes an “ideal copolymerization”
][M
][Mr
]d[M
]d[M
2
11
2
1=
In this case ~M1• and ~M2 • have the
same preference for adding either of the two monomers.
Ideal copolymerization
F
f
Chemistry 367L/392N
Condition under which F, the mole fraction of monomer in the polymer and f, the mole fraction in the feed
remain constant through the whole polymerization….that
is, these ratios are not a function conversion
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
A = styrene
B = butadiene
ra = 0.75, rb = 1.3
F
a (
po
lym
er
co
mp
ositio
n)
fa (monomer composition)
Ideal copolymer
r1=r2= 1.3
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A = styrene
B = maleic anhydride
ra = 0.05, rb = 0.0
F
a (
po
lym
er
co
mp
ositio
n)
fa (monomer composition)
Alternating Copolymer
r1=0.05, r
2=0.0
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
A = vinyl acetate
B = styrene
ra = 0.01, rb = 50
F
a (
co
mp
ositio
n o
f p
oly
me
r)
fa (Composition of monomer)
Rich in one monomer
r1=0.01, r2= 50
Chemistry 367L/392N
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
A = Acrylonitrile
B = Butadiene
ra = 0.046, rb = 0.36
F
a (
po
lym
er
co
mp
ositio
n)
fa (monomer composition)
Quite typical copolymerisation
Azeotropic Composition
r1=0.046, r2= 0.36
Chemistry 367L/392N
F
f
Chemistry 367L/392N
Poly(styrene-alt-maleic anhydride)
OOO
+δ
δ
OOO+
OOO
[ ]n
Charge transfer complex
Chemistry 367L/392N
Charge transfer complex polymerization(alternating copolymer).
H2C CH
R
+ SO2 CH2 CH
R
SO2
CH
R
H2C + CO CH2 CH
R
C
O
Chemistry 367L/392N
rr1 1 > 1, r> 1, r2 2 < 1 or r< 1 or r1 1 < 1, r< 1, r2 2 > 1> 1
10
5
0.5
0.1
If r1 > 1 (k11 > k12) and r2 < 1 (k22 < k21) then M1 is more active than M2 whether either ~M1
* and ~M2*. F1 is
always larger than f1 and the curve is always above the diagonal.
The situation is similar for r1 < 1, r2 > 1 but the curve is below the diagonal.
Chemistry 367L/392N
What is constant here???
This is a bit discouraging!
What is constant here???What is constant here???
This is a bit discouraging!This is a bit discouraging!��
Chemistry 367L/392N
Estimating Reactivity Ratios Estimating Reactivity Ratios
measurement of r1 and r2 is possible by applying the Fineman Rose equation but it is a bit tedious!
Chemistry 367L/392N
Chemistry 367L/392N
Q and eQ and e
� Generalizations:– This is a purely empirical relationship
– Q and e come from measurements of r1 and r2
– Ideal condition is same Q and e values
– Proceeds poorly if Q1 and Q2 are very different
– Tends toward alternating if Q’s are the same and
e’s arelarge but of opposite sign.
Chemistry 367L/392N
Chemistry 367L/392N
I+IV or II+III →
alternating
I+III, II+IV and same →Statistical Copolymers
Χ
Χ I+II or III+IV → Poor Copolymerization
Chemistry 367L/392N
Chemistry 367L/392N
Conclusions-radical copolymers
� Co-polymers are important
– Properties depend on composition
� In general, these materials are
heterogeneous
� Mayo equation allows calculation of composition knowing r1 and r2
� Finemann Ross approach allows determination of r1 and r2
� Alfrey – Price allows estimate of r1 and r2
Chemistry 367L/392N
We discussed A B type step growth polymers -ABABABA-
If is the number of A molecules at the beginning of the
polymerization and is the number if B molecules,
We define r, the stoichiometric imbalance as
What about step growth copolymers??
0
AN0
BN
0
0
B
A
N
Nr =
If p is the conversion (as in Carothers equation) then
fraction of B at p is p or pr and the number of unreacted groups NA and NB is …
0
AN0
BN
0)1( AA NpN −=r
NprNprNB A
B
00 )1()1( −=−=
Chemistry 367L/392N
)(2
1BA NNN +=
At this point, the number of A and B end groups is NA + NB , but 2 ends per chains…the number
N of chains in the jar is….
Which is….
−+−=
r
NprNpN A
A
00 )1()1(
2
1
Or…..
−+= p
r
NN A 2
11
2
0
Now..the total number of repeat units, Nr is ….
)(2
1 00
BAr NNN += One repeat unit formed per reaction
Chemistry 367L/392N
Remember….0
0
B
A
N
Nr = So….
+=
+=
r
rN
r
NNN A
o
Ao
Ar
1
22
1 0
DP is the number of monomer units divided by number of chains
−+
+
==
pr
N
r
rN
N
NDP
A
A
r
21
12
1
20
0
Which luckily reduces to…pr
rDP
21
1
−+
+=
SupplementaryHomework…
Show Algebra
To here!
Chemistry 367L/392N
rpr
rDP
21
1
−+
+=
Note that if there is no stoichiometric imbalance, r =1 and we get…..
This is nice!!!
pDP
−=
1
1 The Carothers Equation!!
When A is totally consumed (p =1) then….
r
rDP
−
+=
1
1