COPOLYMERIZATION
POLYMERIZATION OF TWO OR MORE MONOMERS
Examples:
Poly(ethylene-co-propylene) (EP)
Poly(styrene-co-butadiene) (SBR)
®
Poly(vinylidine chloride-co-vinyl chloride) (Saran )
Microstructure depends on
method of polymerization
B
B A A A A B A
A
B A
B
B
B
A
A
A
B A
A
B
R* B
R*
A B
A B
A
A
B A
B A
A
R* A
B
Random Copolymers
-A-B-B-B-A-A-B-A-B-A-A-A-B-A-B-B-
Alternating Copolymers
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-
Block Copolymers
A-A-A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-A-A-A-A-A-A
POST POLYMERIZATION OR
HOW TO MAKE A GRAFT COPOLYMER
Examples:
High Impact Polystyrene (HIPS)
Acrylonitrile / Butadiene / Styrene (ABS)
-A-A-A-A-A-A-A-A-A-A-
-A-A-A-A-A-A-A-A-A-A-
B-B-B-B-B-B
-B-B-B-B-B-B
-A-A-A-A-A-A-A-A-A-AB
-A-A-A-A-A-A-A-A-A-A- B
B R* B B
B
B -A-A-A-A-A-A-A-A-A-AB
B B
B
B
B
B
-A-A-A-A-A-A-A-A-A-AB
B R*
-B-B-B-B-B-B
B R* B
-B-B-B-B
Dissolve polymer A in a solvent
Add monomer B and initiator
Polymerize
B-B-B-B-B
FREE RADICAL COPOLYMERIZATION
ARE "RANDOM" COPOLYMERS REALLY RANDOM ?
~~~~~~~~~~~ A*
~~~~~~~~~~~ B*
A
B
A
B
~~~~~~~~~~~A -- A*
~~~~~~~~~~~A -- B*
~~~~~~~~~~~ B -- A*
~~~~~~~~~~~ B --B*
DO A's ADD TO A's AS EASILY AS B's ADD TO A's ?
(and vice - versa)
POSSIBLE PRODUCTS
COPOLYMERIZATION OF MONOMERS M 1 AND M 2
•Homopolymers
•Alternating copolymers
•”Ideal" or truly random
copolymers
•Non ideal copolymers tendency to "blockiness”
or alternating
KINETICS OF COPOLYMERIZATION
~~~~~~~~ M 1. + M 1
k 11
~~~~~~~~ M 1 .
~~~~~~~~ M 1. + M 2
k 12
~~~~~~~~ M 2 .
~~~~~~~~ M 2. + M 1
k 21
~~~~~~~~ M 1 .
~~~~~~~~ M 2. + M 2
k 22
~~~~~~~~ M 2 .
TENDENCIES
1. BLOCKS AND / OR HOMOPOLYMER
IF k 11 > k 12 AND
k 22 > k 21
2. ALTERNATING IF
k 12 > k 11
3. RANDOM COPOLYMERS IF
AND k 22 = k 21
AND
k 11 = k 12
k 21 > k 22
REACTIVITY RATIOS
DEFINE
r1 =
k 11
___
k 12
r2
k 22
___
= k
21
WHAT IF
r1 , r2 >> 1 ?
r1 , r2 << 1 ?
r1 = r2
= 1 ?
r1 r2 = 1 ?
KINETICS OF COPOLYMERIZATION
d[ M 1 ]
- ____
= k 11 [ M 1. ][ M 1 ] + k 21 [ M 2. ][ M 1 ]
dt
d[ M ]
- ____2 = k 22 [ M 2. ][ M 2 ] + k 12 [ M 1 . ][ M 2 ]
dt
Divide and eliminate [ M ]. terms using
STEADY STATE ASSUMPTION
.
M, 1. M generated
and consumed
2
at equal rates. we only need focus on one
type of radical; e.g. M 1.
k 12 [ M . ][ M ] = k [ M . ][ M ]
21
1
2
2
1
COPOLYMER EQUATION
d[ M 1 ]
______ =
d[ M 2 ]
[M 1 ]
___
[M 2 ]
{
r1[ M 1] + [ M 2 ]
_____________
[M 1 ] + r2 [ M 2 ]
}
or
d[ M 1 ]
_____ =
d[ M 2 ]
( r1[ M 1] / [ M 2 ]+1 )
________________
( r2 [ M 2 ]/ [M 1 ]+1 )
remember
r1 =
k 11
___
k 12
r2
k 22
___
=
k 21
COPOLYMER EQUATION
It is often more convenient to work
in terms of mole fractions.
define :
F 1 = mole fraction of monomer 1 in
the polymer at some instant of
time
f1
= mole fraction of monomer 1 in
the feed at the same instant of
time
d[ M 1 ]
_____________
F 1 = 1 - F2 =
d[ M 1 ] + d[ M 2 ]
f1 = 1- f
2
=
[M 1 ]
__________
[M 1 ] + [ M 2 ]
COPOLYMER EQUATION
F1
2
=
( r1 - 1 f1) + f1
_________________________________
2
( r1 + r2 - 2)f1 + 2 (1 - r2 ) f 1+ r2
1
r1 > 1 ; r2 < 1
Note that this equation
describes the instantaneous
copolymer composition
r1 < 1 ; r2 < 1
F
1
Azeotrope
r1 = r2 = 1
0
0
f1
In a batch copolymerization composition will "drift "
with conversion . to treat this properly we need to first
do some statistics,but here we will just give a couple of
illustrations
1
DETERMINATION OF REACTIVITY RATIOS
There are some older methods based on rearrangements
of the copolymer equation
LET
[M1]
[M2]
THEN
= x and
d[M1]
d[M2]
= y
r
2
1 + r1x
r2
1+ x
x(r1x + 1)
r2 =
-x
y
y =
r
1
MAYO - LEWIS PLOT
(
x 1 - 1y
( ) = r( )
1
x 1- y
1
x2
y - r2
)
r2 (intercept)
(5.16)
( xy )
2
r1 ( - slope)
FINEMAN - ROSS PLOT
DETERMINATION OF
REACTIVITY RATIOS
ALSO;
KELEN TUDOS PLOT
Q - e SCHEME
APPLICATION OF PROBABILITY
THEORY AND nmr SPECTROSCOPY
POLYMER SYNTHESIS—COPOLYMERIZATION
THE COPOLYMER EQUATION
1 + rAx
y =
rB
1 + x
[A]
[B]
P [A]
y = Composition of the Instaneously Formed Polymer = 1
P [B]
x = Composition of the Feed =
1
Copolymer Composition as a Function of Conversion
Polymer Composition
1.0
VDC
0.8
0.6
0.4
0.2
VC
0.0
0
20
40
60
80
100
Degree of Conversion
Compositional variation for vinylidine chloride/vinyl chloride copolymers.