Chemistry Reference
In-Depth Information
-methyl styrene it cannot be polymerized by free-radical mechanism.
It polymerizes readily, however, by an ionic one. Resins based on copolymers of
Due to the allylic nature of
a
-methyl styrene are
available commercially. Other styrene derivatives that can be obtained commercially are:
a
1. Alkyl or aryl substituted styrenes,
R'
R"
where R
1
and R
2
are alkyl or aryl groups.
2. Halogen derivatives,
X
1
X
2
where X
1
and X
2
¼
F, Cl, Br, or I.
3. Polar-substituted styrenes,
R
where R
CN, CHO, COOH, OCOCH
3
, OH, OCH
3
,NO
2
,NH
2
, and SO
3
H.
Vinyl toluene polymerizes readily by free-radical mechanism at 100
C. The absolute rate at that
temperature is greater than for styrene. The activation energy for vinyl toluene polymerization is
17-19 kcal per mole while that for styrene is 21 kcal mole. This monomer can also be polymerized by
ionic and coordination mechanisms. Earlier attempts at polymerization of
¼
-methyl styrene with
Ziegler-Natta catalysts were not successful [
187
,
188
]. Later, however, it was shown that polymeri-
zation does take place with TiCl
4
/Al(C
2
H
5
)
3
at
a
78
C. The activity of the catalyst and the DP depend
on the ratio of aluminum to titanium, the nature of the solvent, and on the aging of the catalyst [
189
].
The optimum ratio of the aluminum alkyl to titanium chloride is 1.0-1.2. Mixing and aging of the
catalyst must be done below room temperature, and the valence of titanium must be maintained
between 3 and 4 [
189
]. This led Sakurada to suggest that the reaction actually proceeds via a cationic
rather than a coordinated anionic mechanism [
189
].
Various reports in the literature describe cationic polymerizations of
a
-methyl styrene with Lewis
acids [
190
-
192
]. The products are mostly low molecular weight polymers, some containing
unsaturation with pendant phenylindane groups. A high molecular weight polymer can be prepared
from
130
C with AlCl
3
in ethyl chloride or
in carbon disulfide [
193
]. The product has a narrow molecular weight distribution. Some
a
-methyl styrene by cationic polymerization at
90 to
T
g
and
T
m
values of polystyrene-like materials, including isotactic polystyrene, are presented in Table
6.11
.
