Chemistry Reference
In-Depth Information
0.10
1.0
f
2
0.08
0.8
Average F
1
0.06
0.6
F
1
0.04
0.4
f
1
0.02
0.2
0.0
0.0
0.2
0.4
0.6
0.8
0.9
1.0
Degree of conversion
FIGURE 9.3
Drift of copolymer and comonomer compositions with conversion in the copolymerization
of glycidyl methacrylate
(H
2
C
C
C
O
CH
2
C
CH
2
O
O
H
3
C
(M
1
, r
1
5
0.5) with styrene (M
2
, r
2
5
0.4) with f
1
5
0
:
037 (5 wt% of the methacrylate).
Azeotropic composition is at f
1
5
0
:
55
:
9.6
Determination of Reactivity Ratios
The measurement of reactivity ratios appears to be straightforward provided the
equation linking feed and copolymer compositions fits the data obtained by analyz-
ing the compositions of copolymers formed from several different concentrations of
monomers. If a differential form of the copolymer equation (
Eq. 9-31
or
9-14
)is
used with initial feed composition values, it is necessary to keep the total conversion
to polymer in each experiment less than about 5% so as to minimize the drift of
copolymer makeup. Ten or more percent of the monomers can be converted to poly-
mer in a single run without significant calculation error if the arithmetic averages of
the final and initial monomer concentrations are used in these differential copolymer
equations
[4]
. The extent of reaction at which this procedure becomes unreliable
depends on the relative magnitudes of the reactivity ratios, except of course for the
case of azeotropic feed mixtures. This expedient is safe in general so long as the
concentration of each unreacted monomer is linearly related to reaction time
[5]
.
