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418 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

NITROPOLYSTYRENE

Investigations on the nitration of polystyrene go back to 1845, to the experi-

ments of Blyth and Hofmann [39], who reacted boiling nitric acid with glassy

polystyrene, which was obtained from styrene of natural origin, namely from

Styrax resin. The product prepared contained 10.6% of N.

During World War II several authors resumed the investigations. G. B. Bachman

and his co-workers [40] nitrated polystyrene with nitric acid (sp. gr. 1.50) and

obtained products of various degrees of nitration depending on the nitration tem-

perature: at 50°C a product containing 10.0% of N was obtained, while at 150°C

the product contained 11.2% of N.

A vast amount of research was carried out by Zenftman [41], who proved the

action of a nitrating acid on polystyrene to be limited to the nitration of the super-

ficial layer of polymer granules only. The inside of the granules remained unaffected.

A necessary condition for obtaining complete nitration of the substance is to use

a nitrating mixture which completely dissolves the polymer. According to Zenftman,

nitrating mixtures of a composition ranging from the anhydrous one:

HNO 3

H 2 SO 4

to that containing water:

HNO 3

H 2 SO 4

H 2 O

are good solvents for polystyrene.

76%

12%

12%

II

With a mixture of type I, a product containing up to 14.4% of N can be obtained,

while a mixture of type II gives a product with about 9.4% of N.

The nitration of polystyrene is carried out in the following way. To a mixture

containing

HNO 3 73%

H 2 SO 4 26.5%

H 2 O 0.5%

finely ground polystyrene is added, a temperature of 18°C being maintained by

cooling. The polystyrene to acid ratio is 1:20. After all the polymer has been added,

the temperature is allowed to rise to 20°C. After one hour’s stirring the polymer

becomes completely dissolved in acid. After 4 hr from the beginning of the

nitration process the solution is poured into water. Nitropolystyrene is then pre-

cipitated in the form of threads, which are washed with water, ground in a ball

drum and again washed with hot water (90-95°C). From 100 g of polystyrene

nearly 33 g of the nitrated product containing 13.4% of N can be obtained.

It has been shown by analysis that even under the most severe conditions of

nitration only two nitro groups can be introduced into the benzene ring. The

oxidation of nitropolystyrene to the corresponding nitrobenzoic acid (with MnO 2

in sulphuric acid) has shown, according to Zenftman [41], that the substitution