Chemistry Reference
In-Depth Information
k
p
M
n
1
M
!
M
n
1
1
where M
n
is a macroradical with degree of polymerizatio
nn
. The major ter-
mination reaction involves the Ce
1
4
component of the redox system:
k
t
0
M
n
1
Ce
4
Ce
3
1
1
H
1
1
1
!
dead polymer
Using the steady-state assumption, derive a useful expression for the rate
of polymerization. Take the initiator efficiency
f
and assume that the propa-
gation reaction is the only one that uses significant quantities of monomer.
5
8-5
For acrylamide,
k
p
=
22 liter/mol sec at 25
C and termination is by
coupling alone. At this temperature the half-life of isobutyryl peroxide is
9.0 h and its efficiency in methanol can be taken to be equal to 0.3. A
solution of 100 g/liter acrylamide in methanol is polymerized with 10
2
1
M
isobutyryl peroxide.
(a)
k
t
5
What is the initial steady-state rate of polymerization?
(b)
How much polymer has been made in the first 10 min of reaction in 1
liter of solution?
8-6
One hundred liters of methyl methacrylate is reacted with 10.2 mol of an
initiator at 60
C.
(a)
What is the kinetic chain length in this polymerization?
(b)
How much polymer has been made in the first 5 h of reaction?
10
6
liter
k
p
5
5
:
5 liter
=
mol sec
k
t
5
25
:
5
=
mol sec
3
94 g cm
2
3
Density of monomer
0
:
5
t
1
=
2
for this initiator
50 h
f
0
:
3
5
5
8-7
Redox initiation is often used in polymerizations in aqueous systems.
Thus, H
2
O
2
and Fe
2
1
ion can be used to initiate the polymerization of
acrylamide in water. Derive an expression for the steady-state rate of poly-
merization in this case:
k
Fe
2
1
!
HO
1
Fe
3
1
H
2
O
2
1
OH
2
1
8-8
(a)
In a free-radical polymerization in solution the initial monomer
concentration is increased by a factor of 10:
(i)
How is the rate of polymerization affected quantitatively?
(ii)
What change takes place in the number average degree of
polymerization?
(b)
If the monomer concentration was not changed but the initiator con-
centration was halved instead:
(i)
What is the change in the rate of polymerization?
