Chemistry Reference
In-Depth Information
and
R
is the universal gas constant. Calculate
K
1
and the equilibrium con-
centration of H
2
O in the melt at 250
C and use
Eq. (12-8)
.]
12-2
Acrylonitrile has considerable solubility in water, while styrene is negligi-
bly soluble. In the copolymerization of these two monomers in a suspen-
sion process, it is not desirable that much polymerization take place in
solution or emulsion in the aqueous phase, as this will produce material
that differs significantly in molecular weight and structure from that poly-
merized in the monomer droplets. How could you ensure that polymeriza-
tion is confined essentially to the suspended monomer droplets?
12-3
Following is a recipe for the suspension polymerization of styrene to give
polymer beads with diameters about 0.5
0.25 mm. Such products have
surface/mass ratios that are sufficiently high to ensure good dispersion of
dry pigments when the colorants and solid polymer are stirred together.
Aqueous phase: 20 kg demineralized H
2
O, 0.13 kg Ca
3
(PO
4
)
2
(insoluble
suspending agent), 0.15 kg Na
-
6
-naphthalene sulfonate (suspending agent),
and 0.001 kg Na polyacrylate (polymeric suspending agent).
Monomer phase: 17 kg styrene and three initiators, each present in the
amount of about 0.02 mol.
The polymerization is not carried out isothermally but with stepwise
temperature rises. This is because styrene polymerizes relatively slowly. A
mixture of initiators is therefore used, and it has been found useful in this
context to select initiators with half-lives similar to the polymerization
time in a particular temperature range. The following temperature program
has been used:
β
Temperature (
C)
Temperature (
C)
Hours
Hours
0
1
40
80
8
13
90
1
7
13
15
90
110
80
7
8
80
90
15
27
110
Azodiisobutyronitrile is a suitable initiator for the 80
C stage of this
polymerization. Find the most suitable initiators of those listed in
Table 8.1 for the 90 and 110
C intervals. Assume an approximate activa-
tion energy for peroxy-type initiators of 30 kcal mol
2
1
.
12-4
In industrial polymerization, the monomer is often added slowly to the
reaction mixture. Consider the following experiments [J.J. Krackeler and
H. Naidus,
J. Polym. Sci. Part C
27, 207 (1969)] with polystyrene poly-
merizations. The simple recipe is styrene: 32 parts, 4.4% solution of
K
2
S
2
O
8
: 3.4 parts, surfactant solution (containing 7% octyl phenol ethyl-
ene oxide adduct and 1% sodium lauryl sulfate): 58 parts, and reaction
temperature 70
C. Conversion-time plots are shown below for
three
