Chemistry Reference
In-Depth Information
styrene (M
2
) the respective concentrations in the initial monomer droplets are
about 9.4 and 1.9
M
. Since
r
1
5
0.8,
Eq. (9-13)
indicates that the
copolymer formed in the initial stages of the reaction will contain about 78%
by weight of butadiene, compared to 72% of this monomer in the feed.
1.4 and
r
2
5
9.3
Copolymer Structure Inferences from Reactivity Ratios
Before measurements of reactivity ratios are reviewed, it is useful to consider
what the absolute magnitude of these parameters implies. This is most easily
approached from the relation between the
r
1
r
2
product and copolymer structure as
summarized in
Table 9.1
. This table also includes a list of reactivity ratios that
apply in some important free radical polymerizations.
9.3.1
Random Copolymers
According to our reaction scheme M
1
M
1
bonds are formed only by reaction (9-2).
The probability that a radical ending in an M
1
unit adds an M
1
unit is equal to the
rate of this reaction divided by the sum of the rates of all reactions available to this
Table 9.1
(a) Copolymer Structure and r
1
r
2
Product
r
1
r
2
r
1
r
2
Copolymer structure
r
1
1
/r
r
1/
r
1
Random (ideal)
5
5
2
2
1
1
1
0
Alternating
{
{
-
c
1 Tends to be homopolymer of M
1
(b) Some Reactivity Ratios for Radical Copolymerizations
1
1
,
,
M
1
M
2
r
1
r
2
r
1
r
2
Butadiene
Styrene
1.4
0.8
1.1
Ethylene
Vinyl acetate
1.0
1.0
1.0
Vinyl chloride
Vinyl acetate
1.4
0.65
0.9
Vinylidene chloride
Vinyl chloride
3.2
0.3
1
Methyl methacrylate
Methacrylamide
1.5
0.5
0.8
Vinylidene chloride
Acrylonitrile
0.4
0.9
0.4
Styrene
Methyl methacrylate
0.5
0.5
0.3
Butadiene
Methyl methacrylate
0.7
0.3
0.2
Acrylonitrile
Vinyl chloride
2.7
0
0
Acrylonitrile
Styrene
0
0.4
0
Styrene
Maleic anhydride
0
0
0
