Chemistry Reference
In-Depth Information
1.0
0.8
4
3
1
2
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1.0
Mole fraction m
1
in feed, f
1
FIGURE 9.1
Relation between instantaneous feed composition f
1
and corresponding copolymer
composition F
1
for random copolymerizations. Curve 1, ethylene (r
1
5
1)
vinyl acetate
(r
2
5
1); curve 2, styrene (r
1
5
0.8)
butadiene (r
2
5
1.4); curve 3, vinyl chloride
(r
1
5
1.4)
vinyl acetate (r
2
5
0.65); curve 4, vinylidene chloride (r
1
5
3.2)
vinyl chloride
(r
2
5
0.3).
on the feed concentrations and reactivity ratios (
Eqs. 9-13 and 9-14
), and copol-
ymers with different average compositions can be made by altering the feed ratios
in batch reactions.
The vinylidene chloride (M
1
)
vinyl chloride (M
2
) system is an example of a
random copolymerization in which
r
1
5
1. Reasonably
homogeneous copolymers with controlled concentrations of the less reactive com-
ponent can be made in semibatch processes by controlling the monomer feed. In
this case the more reactive ingredient, vinylidene chloride, is added intermittently
or continuously in a proportional manner to a mixture to which all the vinyl chlo-
ride is charged initially.
3.2,
r
2
5
0.3, and
r
1
r
2
D
9.3.2
Alternating Copolymers
If each radical prefers to add the monomer of the opposite type both reactivity
ratios will tend to zero, and the copolymer equation becomes
d
½
M
1
=
d
½
M
2
5
1
(9-19)
or
F
1
5
F
2
5
0
:
5
(9-20)
