RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

50. Study of the Influence of the Purity of 3-Vinyl-9-ethylcarbazole on Its Copolymerization with Divinylbenzene

V. P. Lopatinskii, E. E. Sirotkina, M. P. Grosheva

(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)

Modern technology imposes diverse requirements on ion-exchange resins; in particular, with the development of the atomic industry, a demand has arisen for radiation-resistant ion exchangers. Searches in this direction have shown that the introduction into a copolymer of styrene with divinylbenzene of systems with strongly conjugated bonds of the type of pyridine bases increases the radiation resistance of ion exchangers obtained on the basis of these copolymers [1, 2]. It was therefore of interest to use vinyl derivatives of carbazole for the synthesis of radiation-resistant ion exchangers.

As our investigations, as well as those of other authors [3], have shown, polymers obtained on the basis of vinyl derivatives of carbazole are stable under irradiation.

The present work is part of studies being carried out in the field of the synthesis of ion-exchange resins based on vinyl derivatives of carbazole. The authors used 3-vinyl-9-ethylcarbazole and divinylbenzene to obtain crosslinked copolymers. This communication gives the results of a study of two questions: first, the influence of polymerization inhibitors on increasing the yield of 3-vinyl-9-ethylcarbazole during its purification and, second, the study of the influence of the purity of 3-vinyl-9-ethylcarbazole on the process of copolymerization. 3-Vinyl-9-ethylcarbazole was obtained by reduction of 3-acetyl-9-ethylcarbazole according to a previously developed method [4], which consists in reducing 3-vinyl-9-ethylcarbazole with aluminum isopropylate in xylene solution at a temperature of 135–145°C. After completion of the reduction, the reaction mass was treated with an aqueous alkali solution, and from the xylene layer, after removal of the solvent, the pure monomer was isolated by vacuum distillation, purified by recrystallization from methanol, and analyzed for the content of unsaturated compounds by the Martin method [5]. The yield of pure monomer with m.p. 65–66°C was 20–25% of theoretical. The bulk of the monomer was converted into polymer during its purification by recrystallization. Therefore, the influence of various polymerization inhibitors during the process of monomer purification was studied. The inhibitors used were: hydroquinone, caustic alkalis, anhydrous sodium acetate, copper acetate, basic copper carbonate, and basic copper acetate*).

*) The authors express their deep gratitude to Professor G. N. Khodalevich for kindly providing samples of basic copper acetate.

The best inhibiting properties are possessed by basic cupric acetate, which we studied in greater detail.

When 3-vinyl-9-ethylcarbazole is isolated from the xylene layer by distillation in vacuum, it is possible to obtain the monomer in a yield of about 50% and with an unsaturated-content of 80–90%. However, upon further purification the yield of pure monomer decreases considerably as a result of the polymerization reaction.

As can be seen from Table 1, only fourfold recrystallization from methanol makes it possible to obtain a pure monomer, while the monomer losses

Table 1

Results of experiments on the purification of 3-vinyl-9-ethylcarbazole

amount to more than 70%. Repeated distillation in vacuum only slightly increases the purity of the monomer, while about 90% of the monomer is lost. Purification of the monomer by distillation in vacuum in the presence of basic cupric acetate (in an amount of 0.01% of the weight of the monomer) makes it possible to obtain the monomer in high yield and with a fairly high content of unsaturates (92–95%). Addition of more than 0.01% inhibitor leads to poorer results.

3-Vinyl-9-ethylcarbazole polymerizes very readily; therefore, as impurities it contains low-molecular-weight viscous dimers and trimers. It is known from the literature that, when copolymerization of vinyl monomers with divinyl monomers is carried out in the presence of inert (third) components, macroporous crosslinked copolymers possessing greater mechanical strength are obtained [6]. As third components, it is recommended to use, along with solvents, low-molecular-weight polymer fractions, which are subsequently removed from the crosslinked copolymers by washing with solvents. When 3-vinyl-9-ethylcarbazole is isolated by distillation in vacuum (205–210°C, 3–4 mm Hg), 10–20% of low-molecular-weight polymers is always formed in it. It was of interest to use 3-vinyl-9-ethylcarbazole with various contents of low-molecular-weight polymers for copolymerization. Divinylbenzene was used as the crosslinking agent in an amount of 10% of the weight of the monomers. The reaction was carried out in the presence of azobisisobutyric acid dinitrile, which in all cases was taken in an amount of 2% of the weight of the monomers. As stabilizer, appli-

an aqueous solution of polyvinyl alcohol or starch was used. It was noted that the use of aqueous solutions of polyvinyl alcohol with concentrations below 2% has an unsatisfactory effect on the shape of the granules. Good results were obtained when 3–4% solutions of polyvinyl alcohol were used. However, the best grain shape, with the smallest scatter in granule size, was obtained when 2–3% aqueous starch solutions were used.

The ratio of the aqueous phase to the hydrocarbon phase in these experiments was from 6 : 1 to 4 : 1. The use of other ratios leads to agglomeration of the granules.

The copolymerization reaction was carried out in a flask with a hemispherical bottom, equipped with a stirrer, thermostat, reflux condenser, and dropping funnel, placed in a thermostat. The reaction temperature was regulated with an accuracy of \(\pm 0.1^\circ\mathrm{C}\). Ten to fifteen minutes before the start of the reaction, the hydrocarbon phase was prepared by dissolving 3-vinyl-9-ethylcarbazole and the initiator in divinylbenzene. It was added, with stirring, to the aqueous phase at a temperature of \(70^\circ\mathrm{C}\), which was maintained until the end of the reaction. The end of the reaction was determined by the hardening of the granules, which required 6–7 hours. After this the polymer was filtered off, washed with water, and then with alcohol and xylene to remove unreacted monomers and uncrosslinked polymers. The washed polymer was dried, fractionated, and analyzed.

Table 2

Effect of the purity of 3-vinyl-9-ethylcarbazole on the copolymerization process

As can be seen from the data in Table 2, 3-vinyl-9-ethylcarbazole with a polymer content of no more than 5% can be successfully used for copolymerization. At a higher polymer content in 3-vinyl-9-ethylcarbazole, agglomeration of the granules occurs. This is explained by the fact that low-molecular-weight polymers of 3-vinyl-9-ethylcarbazole are viscous oils and play the role of a plasticizer in which the copolymer granules swell.

By sulfonation of the copolymer obtained, a sulfocation exchanger with good exchange capacity was obtained. The results of these studies will be presented in the next communication.

Conclusions

1. The inhibiting action of copper acetate on the polymerization process of 3-vinyl-9-ethylcarbazole during its purification by distillation in vacuum has been established.

1. It has been shown that, in order to obtain crosslinked copolymers, it is necessary to use 3-vinyl-9-ethylcarbazole with an impurity content of not less than 95%.

REFERENCES

1. Investigation of the Properties of Ion-Exchange Materials. Collection, Nauka Publishing House, 1964.
2. E. V. Egorov, P. D. Novikov. The action of ionizing radiation on ion-exchange materials. Atomizdat, 1965.
3. R. Bolt, D. Carroll. The action of radiation on organic materials. Atomizdat, 1965.
4. V. P. Lopatinskii, E. E. Sirotkina. Proceedings of the Tomsk Polytechnic Institute, 136, 26, 1965.
5. R. Martin. Anal. Chem., 21, No. 8, 921—922, 1949.
6. I. Seidl, J. Malinsky, K. Dušek. Plasticheskie Massy, No. 12, 7, 1963.