RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

49. Study of the Copolymerization of 9-Vinylcarbazole with Styrene and Divinylbenzene

V. P. Lopatinskii, E. E. Sirotkina, S. I. Kudinova

(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)

Literature data show that polymers and some copolymers of 9-vinylcarbazole possess high resistance to the action of large doses of radiation [1, 2] and to the action of elevated temperature [3, 4]. On this basis, one may expect that replacement of part of the styrene groups in the copolymer of styrene with divinylbenzene by 9-vinylcarbazole groups will lead to an increase in the radiation resistance and heat resistance of cross-linked copolymers used in the synthesis of ion-exchange resins.

In the present work, the suspension copolymerization of 9-vinylcarbazole with styrene and divinylbenzene in the presence of free-radical initiators was studied. The influence of temperature, initiator concentration, changes in the ratio of the monomer and aqueous phases, emulsifier concentration, and purity of 9-vinylcarbazole was investigated.

Of the two initiators tested—benzoyl peroxide and dinitrile of azodiisobutyric acid—the latter proved to be the better one; consequently, the influence of other factors was studied in its presence. The optimum copolymerization conditions were usually determined at a constant monomer ratio: 9-vinylcarbazole—20%, styrene—70%, divinylbenzene—10%. However, in a number of experiments the monomer ratio was changed, and copolymerization was carried out in systems containing from 10 to 80% 9-vinylcarbazole, while the amount of divinylbenzene remained equal to 5 and 10% of the weight of the monomer phase (Tables 1 and 2).

Polyvinyl alcohol and starch were used as emulsifiers. The best results were obtained when using polyvinyl alcohol solutions with a viscosity of 1.5–1.7 cP and starch with a viscosity of 1.1–1.2 cP.

The study of the effect of the amount of initiator on the copolymerization process was carried out at 60°C. As can be seen from Fig. 1, with an increase in the amount of initiator, the duration of the reaction decreases. However, when the initiator content is more than 1.5%, the nitrogen released during its decomposition causes the appearance of small bubbles in the polymer granules. A reduction in the duration of the process can also be achieved by increasing the copolymerization temperature, as a result of which it becomes possible to reduce the amount of initiator. Thus, copolymerization is completed in 6 hours at 60°C with an initiator amount of 1.5%, or at 80°C with an initiator amount of 0.5%.

The weight ratio of the monomer and aqueous phases was varied from 1:1 to 1:4. Copolymer granules homogeneous in size and of regular spherical shape were obtained at phase ratios of 1:3 and 1:4. At other ratios the size heterogeneity of the granules increases.

Table 1

Effect of the monomer ratio on the copolymer yield (reaction temperature 60°C, amount of initiator 1.5%, emulsifier—polyvinyl alcohol)

Table 2

Effect of the monomer ratio on the copolymer yield (reaction temperature 80°C, reaction duration 6 hours, emulsifier—starch)

In experiments on the effect of the amount of cross-linking agent—divinylbenzene (DVB)—on the copolymerization process, a dependence was established between the concentration of DVB in the monomer phase and the swelling of the copolymer (Fig. 2). With a DVB content of less than 5%, strong granules cannot be obtained.

An increase in the content of 9-vinylcarbazole in the monomer phase leads to an increase in the reaction duration (Fig. 1), which can be reduced either by introducing a larger amount of initiator or by raising the temperature. However, under all conditions and contents-

when the content of 9-vinylcarbazole is more than 40%, the mechanical strength of the granules decreases noticeably. As can be seen from the data in Tables 1 and 2, the amount of 9-vinylcarbazole that did not enter into the reaction ranges from 4 to 6%.

Fig. 1. Dependence of the copolymerization duration on the amount of initiator (temperature 60°C)

The total amount of unsaturated components is 8–10%; however, as the amount of 9-vinylcarbazole in the initial charge increases, the yield of copolymer decreases. Balance experiments showed that in this case the weight of the dry residue from the xylene solution increases, i.e., the yield of uncrosslinked polymers increases.

All the studies described above were carried out using 9-vinylcarbazole of 99–100% purity. Special experiments established that, in the presence of azodiisobutyronitrile, 95% 9-vinylcarbazole can be successfully used in the copolymerization, which considerably reduces the requirements for its purification.

Fig. 2. Swelling of the copolymer as a function of the concentration of divinylbenzene (DVB) in the monomer phase (9-vinylcarbazole content 20%, divinylbenzene—0.5%)

Experimental Part

Starting reagents

Styrene, a rectified product, was washed free of stabilizer before polymerization and distilled under vacuum.

Divinylbenzene from the Kemerovo “Karbolit” plant was preliminarily purified by vacuum distillation and by washing the stabilizer out with alkali. DVB containing, on average, 25–45% divinyl derivatives was used. When preparing the hydrocarbon charge before polymerization, the content of monovinyl derivatives in DVB was taken into account.

Azodiisobutyric acid dinitrile was purified by recrystallization from ethyl alcohol. Emulsifiers: polyvinyl alcohol, grade TUM 582/55, and soluble starch, GOST 10163-62.

9-Vinylcarbazole was obtained by a method developed by us earlier and had an unsaturation (by the oxime method [5]) of 99–100%. It was purified by recrystallization from methanol.

Synthesis of a copolymer of 9-vinylcarbazole with styrene and divinylbenzene

The aqueous phase was prepared by boiling a solution obtained from 6.5 g of starch, stirred into 20 ml of cold water and 190 ml of hot water.

The monomer phase was prepared 10–15 minutes before the start of the reaction and consisted of 10 g of 9-vinylcarbazole dissolved in a mixture of 35.5 g of styrene and 8.9 g of divinylbenzene. After complete dissolution of the 9-vinylcarbazole, 0.25 g of azodiisobutyric acid dinitrile was added to the monomer mixture.

The aqueous phase was introduced into a round-bottom flask equipped with a reflux condenser, dropping funnel, stirrer, and placed in a thermostat. The temperature in the thermostat was raised to 80°C, after which the stirrer was switched on at 300–400 rpm, and the hydrocarbon phase was added dropwise. Copolymerization with continuous stirring was continued for 6 hours. The copolymer granules were filtered through nylon fabric and washed with 500 ml of water. To remove unreacted monomers and uncrosslinked polymers, the copolymer was first treated with 100 ml of ethyl alcohol at the boiling temperature for 0.5 hour; the granules were filtered off and treated with 150 ml of xylene on a boiling water bath for 1 hour. The granules were then filtered off, dried at 60°C, and analyzed. The yield of copolymer was 89% of theoretical.

Analyses. Found, %: N 1.3, which corresponds to 89.7% of the 9-vinylcarbazole contained in the initial charge.

Swelling in xylene: 2.8 ml/g.

The alcohol and xylene solutions were analyzed by the oxime method [6] for the content of 9-vinylcarbazole that had not entered into the reaction; the total unsaturation number (according to Martin [7]) and the weight of the dry residue after evaporation of the alcohol and xylene were determined.

Special experiments showed that the copolymers obtained can be used to prepare sulfonic cation exchangers and strongly basic anion exchangers.

Conclusions

1. The granular copolymerization reaction of a three-component system (9-vinylcarbazole, styrene, divinylbenzene) in the presence of azodiisobutyric acid dinitrile has been studied.

2. A method has been developed for preparing crosslinked copolymers based on 9-vinylcarbazole, styrene, and divinylbenzene.

REFERENCES

1. G. Waddington. J. Oil a. Col. Chem. Ass., 44, 179, 1961; Khimiya i tekhnologiya polimerov, No. 10, 138, 1961.

2. R. Bolt, D. Carroll. The Effect of Radiation on Organic Materials. Atomizdat, 1965.

3. E. Barg. Technology of Synthetic Plastics. GKhI, 1954.

4. P. V. Lukin. Chemistry of Monomers, Vol. 1. Izd. inostr. lit., 1960.

5. V. P. Lopatinckii, E. E. Sirotkina, I. P. Zherebtsov, M. A. Leiman. Methods for the Preparation of Chemical Reagents and Preparations, IREA, issue 11, 37, 1964.

6. M. F. Shostakovskii. Simple Vinyl Ethers. Academy of Sciences of the USSR, 1952.

7. R. Martin. Anal. Chem., 21, No. 8, 921–922, 1949.