RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

67. Polymerization of 9-vinylcarbazole

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

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

Poly-9-vinylcarbazole (PVK) is used to obtain heat-resistant dielectrics [1], and in recent years also for the preparation of photosensitive electrophotographic layers [2].

It is known that the polymerization of 9-vinylcarbazole (9-VK) can be carried out in bulk, in solutions, emulsions, and suspensions [3–5]. Naturally, different methods of initiation and different conditions for carrying out the polymerization of 9-VK lead to polymers differing in molecular-weight distribution and in properties. In this connection, it was of definite interest to carry out a comparative evaluation of the electrophotographic properties of PVK obtained by different methods, since such data are absent from the literature. We carried out the polymerization of 9-VK by various methods in the presence of radical- and ionic-type catalysts.

In work [6] it was indicated that 9-VK was obtained by pyrolysis in vacuum of the product of addition of vinyl acetate to carbazole, with a yield of not more than 40%. A more thorough study of this process showed that the synthesis of 9-VK is better carried out without isolating and purifying the addition product. In this case 9-VK is obtained in a purer form, and its yield increases to 80%.

Table 1 presents data on the polymerization of 9-VK in bulk, in solution, and in suspension in the presence of azobisisobutyric acid dinitrile (AIBN) and stannic chloride. The conversion of monomer into polymer was determined from the amount of free monomer by the mercury acetate addition method [7], which is best introduced in the form of its solution in methanol [8].

As is evident from the data presented, the polymerization of 9-VK in bulk and in suspension proceeds at high rates. The degree of conversion of monomer into polymer increases especially rapidly during the first two hours of reaction and amounts to 90.75% and 81.5% for bulk and suspension polymerization, respectively. Subsequently, the degree of conversion (in bulk) changes only very slightly. The overall rate of reaction increases with increasing concentration of initiator in the initial reaction mixture.

As polymerization proceeds, the intrinsic viscosity remains constant. A decrease in viscosity is observed with an increase in the ...

amount of initiator, which is consistent with the theory of radical polymerization.

Table 1

Polymerization of 9-vinylcarbazole

Note: —monomer concentration, 1.25 mol/l.
*—monomer concentration, 0.088 mol/l.

In the polymerization of 9-VK in a toluene solution with DAK, the conversion was determined by taking samples at definite time intervals. The reaction rate was judged from the conversion of the monomer into polymer over time. As can be seen from the data presented, conversion increases to a certain optimum value. The intrinsic viscosity in this case also does not change. A comparison of the intrinsic viscosity of PVK shows that the viscosity of the polymer obtained in toluene is considerably lower than the viscosity of PVK obtained in bulk and in suspension. Apparently, in the polymerization of 9VK in toluene, the solvent plays a major role in the termination of the macromolecular chain.

Polymerization of 9VC was carried out in benzene and dichloroethane (DCE) solution at 25° in the presence of stannic chloride. The catalyst was used as a solution in benzene and DCE. Conversion of monomer to polymer was determined analytically with mercuric acetate and gravimetrically from the polymer yield. The difference between parallel determinations did not exceed 1%.

As can be seen from the data presented, in the presence of stannic chloride it is possible to obtain, in a relatively short time, polymer in high yield (85–90%); moreover, less thermal energy is required to initiate the process than in radical-type polymerization. These data also show that, under comparable conditions, the conversion of 9VC in DCE is higher than in benzene. Apparently, this is connected with the greater solvating ability of DCE compared with benzene. For styrene, for example, an analogous dependence is observed [9]. Measurements of the characteristic viscosity showed that it is higher for PVC obtained in DCE.

Our results confirm the data of Sargent [10], who evaluated solvents with respect to the molecular weights of 9VC polymers obtained with boron fluoride etherate (DCE >> benzene).

Measurements of the electrographic properties of PVC showed that the polymers have a charge potential (400–450 volts) and photosensitivity \((3—5.0 \cdot 10^{-4}\ \text{lux}\cdot \text{sec})\). Noteworthy is the fact that these properties do not depend on the molecular weight of the polymer.

X-ray diffraction patterns of PVC, taken on a URS-50, showed that the polymers have a predominantly amorphous structure with a very slight degree of crystallinity.

IR absorption spectra, recorded on an IKS-14 spectrophotometer in the range 680–4850 \(\text{cm}^{-1}\), showed that the character of the absorption bands of the polymers obtained is the same.

Experimental Part

Synthesis of 9VC. Into a three-necked flask fitted with a stirrer and thermometer are charged 100 g of carbazole, 40 ml of acetone, and 82.5 ml of vinyl acetate. The flask is placed in a cryostat, cooled to 20–18° below zero, 5 g of caustic potash is added, and the mixture is then kept at the same temperature for 25–30 minutes. After completion of the reaction, the catalyst is filtered off; acetone is distilled from the filtrate, and the residue is distilled in vacuo at 180–190°/3–5 mm. The monomer distills as a colorless transparent liquid, rapidly crystallizing into a white solid. The yield is 85–90 g (75–80% of theory).

Purification of the monomer is carried out by crystallization from ethanol and n-hexane. 9-VC has m.p. 64–65°C with a content of the main substance of 99.8–99.9%, determined by the methods of hydrological oximation [11] and addition of mercuric acetate [12].

Polymerization of 9VC in bulk. Polymerization of 9VC was carried out in glass ampoules of 15 ml capacity, which, after charging with the required amount of monomer and initiator (DAK), were sealed in an atmosphere of nitrogen after double evacuation and purging with nitrogen.

Polymerization of 9VC in solution. Polymerization of 9VC was carried out in benzene and dichloroethane solution. Stannic chloride was preliminarily distilled and used as a solution in benzene and DCE (0.8% solution).

The flask with the reaction mixture was fitted with calcium chloride tubes. The resulting polymers were isolated by precipitation with ethanol,

the precipitate was filtered off, washed with alcohol, dried, and the polymer yield was determined.

Polymerization of 9-VC in suspension. Polymerization was carried out in an aqueous-starch suspension in the presence of DAK. The ratio of the aqueous and monomer phases was 20:1. The initiator was introduced as its solution in ethanol (1% solution). The granules obtained were filtered off, washed with hot water, and dried at 50° (740 mm). They were then dissolved in DCE and precipitated with an equal volume of ethanol; the precipitate was transferred to filters, washed with alcohol, dried to constant weight, and the polymer yield was determined.

Viscometric measurements were carried out in an Ubbelohde viscometer in a benzene solution at 25°.

The melting point of the polymers was determined in a capillary; for all polymers it is 230-250°.

For measuring electrophotographic properties, the known method [13] was used.

Films of polyvinylcarbazole on a metal substrate were prepared by casting from a 10% solution in benzene or dichloroethane.

Conclusions

1. A simple and accessible method has been developed for obtaining 9-vinylcarbazole in high yield by pyrolysis of 9-($\alpha$-acetoxyethyl)carbazole in vacuum.

2. The polymerization of 9-vinylcarbazole in bulk, in solution, and in suspension in the presence of azobisisobutyric acid dinitrile and stannic chloride has been studied.

3. The electrophotographic characteristics of poly-9-vinylcarbazoles have been determined, and it has been shown that they do not depend on the methods of polymerization of the monomer.

References

1. H. R. Jacobi. Kunstoffe, 43, 381 (1953).

2. I. B. Sidaravichus. Problems of Radio Electronics, series XII, issue 25, 105 (1964).

3. U.S. patent 2072465, 1937.

4. I. Hughes, A. North. Transaction of the Faraday Society, No. 523, 62 (1966).

5. U. Davidge. British patent 831913, 1960; C. A. 54, 16925, 1960.

6. Yu. P. Shekhirev. Candidate dissertation, Tomsk, 1965.

7. Yu. P. Ponomarev, V. N. Dmitrieva, V. D. Bezuglyi. Journal of Analytical Chemistry, 18, 654 (1963).

8. I. Djonson, I. Fletcher. Analyt. Chem., 31, 1563 (1959).

9. E. B. Lyudvig, A. R. Gantmakher, S. S. Medvedev. Internat. Sump. Macromolecules, Wiesbaden, Section III, Paper A12 (1959).

10. D. Sargent. U.S. patent 2560251.

11. I. P. Zherebtsov. Candidate dissertation, Tomsk, 1967.

12. R. Martin. Analyt. Chem., 21, No. 2, 921 (1949).

13. I. B. Sidaravichus. Candidate dissertation, Vilnius, Lithuanian SSR, 1967.