Chemistry Reference
In-Depth Information
The above condensation takes place in dichloroethane, with stannic chloride catalyst at 50
C[
210
]. The
maximum reaction rate varies with both, the initial concentration of 1,4-dimethyl-2,5-dichloro-
methylbenzene, shown above, and the initial concentration of SnCl
4
. Cross-linked polystyrene particles,
or beads also form by Friedel-Craft suspension cross-linking of polystyrene with 1,4-dichloromethyl-2,5
dimethyl-benzene [
211
]. The polymer is dissolved in nitrobenzene and a two-phase reaction occurs in 70%
by weight of an aqueous suspension of ZnCl
2
. Poly(vinyl alcohol) can be used as the suspending agent.
9.4.3.5 Sulfonation Reactions
Sulfonation reactions of polystyrene and its copolymers with divinyl benzene are carried out
commercially to prepare ion exchange resins. Partial sulfonations of polystyrenes are achieved in
the presence of ethers. When more than 50% of the aromatic rings are sulfonated, the polymers
become water-soluble. At lesser amounts of sulfonation, 25-50%, the polymers are solvent-soluble
[
212
,
213
].
When polystyrene is sulfonated in chlorinated hydrocarbons with a complex of dioxane-SO
3
, the
polymer precipitates from solution at low concentrations [
214
,
215
]. Complexes of ketones with SO
3
can also be used to sulfonate polystyrene in halogenated solvents [
216
]. The ratio of sulfonation is
more favorable for poly(vinyl toluene) than it is for polystyrene at the same conditions [
217
]. Also,
sulfur dioxide swells polystyrene. The polymer can be sulfonated in this medium with sulfur trioxide
or with chlorosulfonic acid [
218
]. Polystyrene, sulfonated in CS
2
with aluminum chloride catalyst, is
water-insoluble in a free acid form [
219
].
9.4.3.6 Nitration, Reduction, and Diazotization
Nitration of polystyrene was originally carried out a long time ago [
220
]. A nitrating mixture of nitric
and sulfuric acids dissolves the polymer and a nitro derivative forms at 50
C within 3 h [
221
]:
NO
2
H
2
SO
4
+
HNO
3
NO
2
The reaction is accompanied by a loss of molecular weight. Nitration of isotactic polystyrene
yields a more crystalline product (about 1.6 NO
2
/ring) than the parent compound [
222
]. Here too,
however, a loss in molecular weight accompanies the reaction [
223
]. Polystyrene can be nitrated
under mild conditions using acetyl nitrate. The product contains approximately 0.6 nitro groups per
each benzene ring [
224
].
The nitro groups of polynitrostyrene are reduced by phenyl hydrazine that acts as a hydrogen
donor [
225
]:
