RESEARCH IN THE FIELD OF CARBAZOLE CHEMISTRY.

102. STUDY OF THE MOLECULAR-WEIGHT DISTRIBUTION OF 9-VINYLCARBAZOLE TELOMERS BY PRECIPITATION CHROMATOGRAPHY

V. I. Berzin, E. E. Sirotkina, V. P. Lopatinsky, V. M. Sutyagin

(Submitted by the Scientific-Methodological Seminar of the Organic Departments
of the Faculty of Chemical Technology)

The kinetics of the radical telomerization of 9-vinylcarbazole (9-VC) in halogen-containing methanes was studied earlier [1]. However, the study of telomerization cannot be considered complete without elucidating the molecular-weight distribution (MWD), which is one of the principal characteristics of a polymer. In this connection, in the present work the MWD of 9-VC telomers was studied by precipitation chromatography.

Experimental Part*

For the study, telomers obtained by polymerization of 9-VC in the medium of active chain-transfer agents (carbon tetrachloride, bromoform, iodoform, carbon tetrabromide, chloroform) under the action of azobisisobutyronitrile dinitrile were taken [1].

Fractionation of the telomers was carried out on a column with a constant temperature gradient of \(2^\circ/1\) cm. The temperature at the top of the column was \(60^\circ\), at the bottom \(15^\circ\). The solvent was benzene, the precipitant ethanol. The average fractionation rate was 20 ml/h. As the packing, a fraction of crushed glass was used that had passed through a sieve with 0.2 mm openings and remained on a sieve with 0.1 mm openings. The experiment and processing of the fractionation results were analogous to the procedure [2].

The molecular weight of the isolated fractions was determined by the “end-group” methods [3] and by isothermal distillation [4], which gave quite satisfactory agreement of results. Analysis for halogen content (chlorine, bromine, iodine) was carried out by the procedure [5]. The experimental data are presented in the form of integral and differential MWD curves.

Discussion of Results

In accordance with the theory of radical polymerization, when weakly active chain-transfer agents (for example, chloroform) are used, a mixture of telomer homologs with high molecular—

* Student T. Mokhova took part in the experimental work.

weight and high polydispersity. Indeed, experimental data on the fractionation of 9-VC telomers (molecular weight 7300) synthesized by telomerization of the monomer in chloroform (Fig. 1) show that the product contains fractions with molecular weights from 2000 to 16000, i.e., it is polydisperse. The latter explains the absence, on the differential curve, of a region with a narrow MWD.

As a result of fractionation of 9-VC telomers obtained in the medium of chain-transfer agents that are most active in comparison with chloroform, it was established that the samples studied have a narrow MWD in different molecular-weight regions.

The largest weight content falls to the share of fractions with molecular weights from \(4 \cdot 10^3\) to \(9 \cdot 10^3\) (about 58%) upon fractionation of the telomer synthesized in carbon tetrachloride (Fig. 2). When carbon tetrabromide is used as the telogen (Fig. 3), telomer homologues are formed with a narrow MWD in the molecular-weight region from \(3.5 \cdot 10^3\) to \(5 \cdot 10^3\) (61 wt%). It follows from Fig. 4 that the greatest weight amount (about 57%) falls on fractions with molecular weights from \(2 \cdot 10^3\) to \(3.5 \cdot 10^3\) in the telomerization of the monomer in bromoform. The presence of a sharply expressed maximum on the differential curve (Fig. 5) indicates low polydispersity of the telomers obtained in the presence of iodoform in a narrowly limited molecular-weight region \((1 \cdot 10^3—2 \cdot 10^3)\).

Fig. 1. Integral (1) and differential (2) MWD curves of the 9-VC telomer \((M_n = 7300)\), synthesized in chloroform.

Conclusions

By the method of precipitation chromatography, molecular-weight distribution curves were obtained for 9-vinylcarbazole telomers synthesized in halogen-containing methanes (carbon tetrabromide, bromoform, iodoform, carbon tetrachloride, chloroform) under the action of azobisisobutyronitrile, and it was shown that the MWD of the telomers is directly dependent on the activity of the chain-transfer agent used.

LITERATURE

1. V. I. Berzin. Author’s abstract of a Candidate dissertation. Tomsk, 1972.
2. A. I. Shatenshtein et al. Determination of the Molecular Weights of Polymers, Moscow—Leningrad, “Khimiya,” 1964.
3. R. Houwink, A. Staverman. Chemistry and Technology of Polymers. Moscow—Leningrad, “Khimiya,” 1965.
4. Methods of Polymer Research. Edited by A. N. Pravednikov. Moscow, IL, 1961.
5. R. D. Glukhovskaya, N. A. Ugol’nikov, Z. M. Murav’eva. Izvestiya TPI, 92, 169, 1960.

Fig. 2. MWD curves of the 9-VK telomer \((M_n — 6700)\), obtained in carbon tetrachloride. 1 — integral curve; 2 — differential curve

Fig. 3. Integral (1) and differential (2) curves of the 9-VK telomer \((M_n — 2800)\). Telogen — carbon tetrachloride

Fig. 4. MWD curves of the 9-VK telomer \((M_n — 2500)\), synthesized in bromoform. 1 — integral curve; 2 — differential curve

Fig. 5. Integral (1) and differential (2) curves of the 9-VK telomer \((M_n — 4200)\), obtained in the presence of iodoform