STUDY OF THE PLASTICIZING PROPERTIES OF CERTAIN CARBAZOLE DERIVATIVES

R. M. KESSENIKH, G. V. TRIPPEL

(Presented by the Scientific Seminar of the Organic Departments)

The study whose results are presented in this article was aimed at determining the plasticizing properties of new organic compounds based on carbazole, obtained in the Problem Laboratory of Polymers of the Tomsk Polytechnic Institute: 9-octylcarbazole and 3-acetyl-9-octylcarbazole. It is a component part of the work being carried out by the Problem Laboratory to find ways of efficiently processing carbazole—an at present unused waste product of the coke-chemical industry. Polyvinyl chloride was chosen as the material to be plasticized—a widespread rigid-chain polar polymer, the most convenient in its physico-mechanical properties for plasticization and processing. In order to compare the plasticizing properties of the new liquids and those already used in industry under identical conditions, all determinations for the new liquids were repeated also for one of the widely used plasticizers—dibutyl sebacate.

Samples of plasticates with plasticizer contents of 0, 2, 5, 10, 25, 45, 65, and 100 percent by weight were obtained by pressing mixtures of polyvinyl chloride powder with an amount of plasticizer corresponding to the composition of the formulation, after preliminary swelling of the mixture in the hot state for 6 hours.

Thermomechanical curves were obtained on dynamometric balances developed by V. A. Kargin and co-workers [1], by the differential method (under an intermittent loading regime). The rate of temperature change was \(60^\circ/\text{hour}\). Measurements were carried out in the temperature interval from \(-80\) to \(+200^\circ\text{C}\). The load on the specimen during measurement was \(40\ \text{g}/\text{mm}^2\).

Discussion of Results

Figures 1 and 2 show the thermomechanical curves obtained for plasticates with dibutyl sebacate and 9-octylcarbazole. Table 1 gives the values of the glass-transition and flow temperatures found from these curves, and the efficiency numbers of the plasticizers. The efficiency numbers…

...tivity were determined from thermomechanical curves obtained for plastics with 1 mol% plasticizer [2], by the decrease in the glass-transition temperature. Figure 3 shows the curves of viscosity versus temperature obtained with an Ostwald viscometer [3].

The effectiveness of carbazole-based liquids is higher than the effectiveness of DBS. This is probably explained by the fact that the bulky carbazole nuclei, inserting themselves between the polyvinyl chloride molecules, greatly weaken their interaction. Attachment of an acetyl group to the molecule of 9-octylcarbazole enhances this shielding effect.

Fig. 1. Thermomechanical curves for PVC + DBS compositions, in which the following amount of plasticizer, in parts by weight, is present per 100 parts by weight of PVC:

Curve No. 1—0 parts by weight;
No. 2—2 parts by weight;
No. 3—5 parts by weight;
No. 4—10 parts by weight.

Curve No. 5—25 parts by weight;
No. 6—45 parts by weight;
No. 7—65 parts by weight;
No. 8—100 parts by weight.

Carbazole at room temperature—

Fig. 2. Thermomechanical curves for PVC + 9-octylcarbazole compositions, in which the following amount of plasticizer, in parts by weight, is present per 100 parts by weight of PVC:

Curve No. 1—0 parts by weight;
No. 2—2 parts by weight;
No. 3—5 parts by weight;
No. 4—10 parts by weight.

Curve No. 5—25 parts by weight;
No. 6—45 parts by weight;
No. 7—65 parts by weight;
No. 8—100 parts by weight.

temperature—is a solid substance \((t_{\mathrm{m}} = 247^\circ\mathrm{C})\). Attachment of an aliphatic radical in the 9-position leads to the formation of a compound with a much lower melting point. Attachment of an additional acetyl group in the 3-position leads to an increase in the viscosity of the liquid (Fig. 3), but should increase its polarity and, consequently, its compatibility with PVC.

It was not possible to determine the compatibility of the plasticizers with polyvinyl chloride by the method of establishing the coagulation threshold, owing to the absence of a suitable precipitant satisfying the required conditions [4].

For carbazole-based liquids, a slight decrease in viscosity is observed in the high-temperature region; liquids with such

Table 1

plasticizers based on them poor frost resistance [5].

It follows from Table 1 that \(T_{\mathrm{g}}\), \(T_{\mathrm{f}}\), and the elastic range vary nonlinearly depending on the plasticizer content in the plasticate. Small additions of plasticizer (up to 2 percent by weight) sharply reduce \(T_{\mathrm{g}}\) and \(T_{\mathrm{f}}\), leaving the magnitude of the elastic range unchanged. Further addition of plasticizer (up to 5%) greatly raises the flow temperature (even exceeding the value of \(T_{\mathrm{f}}\) of the original polymer), while the glass-transition temperature remains unchanged, or even increases slightly. Then, with further addition of plasticizer, \(T_{\mathrm{g}}\) and \(T_{\mathrm{f}}\) decrease, and the elastic range at a certain concentration reaches its maximum value, after which it narrows again.

We attempted, by means of X-ray structural analysis, to elucidate the phenomena occurring during plasticization. The X-ray diffraction patterns (Fig. 4) were taken on a URS-50-I type unit, with a copper anode, \(U_a = 25\ \mathrm{kV}\); \(J_a = 8\ \mathrm{mA}\). The X-ray diffraction patterns contain two maxima at \(2\Theta = 16^\circ\) and at \(2\Theta = 24^\circ\). The X-ray diffraction patterns show that changes occur in the structure of the plasticate as the content of the plasticizing liquid increases.

Additions of plasticizer up to 2 percent strongly reduce intermolecular interaction and, consequently, the overall viscosity of the system. This leads to additional crystallization and ordering of the structure—the maxima in X-ray diffraction patterns 2 and 3 (Fig. 4) become sharper than in pure PVC.

Upon addition of plasticizer, the maxima shift toward larger angles, which corresponds to a decrease in the interplanar distance associated with these maxima. In this case, small additions of plasticizers cause changes mainly in the maximum at \(24^\circ\), and larger additions cause a change in the maximum at \(16^\circ\). If it is assumed that the maxima correspond to the supramolecular structure of the polymer [6], then the phenomena occurring at plasticizer additions of up to 2.5% and higher can be explained by additional ordering of molecules within bundles and ordering of bundles in the volume of the sample, which causes densification of the substance, a certain increase in \(T_{\mathrm{g}}\) at 5 wt.%, and an increase in the flow temperature, which is influenced by crystallization processes; this confirms V. A. Kargin’s conclusions regarding additional crystallization of a polymer at small plasticizer additions [7]. With a further increase in the plasticizer content, the overall viscosity of the system falls, and \(T_{\mathrm{g}}\) and \(T_{\mathrm{f}}\) also fall. The circumstance that the sharpness of the maximum at \(16^\circ\) increases in this case cannot be explained (Fig. 4, X-ray diffraction patterns 5, 7, 8, 10, 12). At very large amounts of plasticizer, the maxima again become diffuse (Fig. 4, X-ray diffraction patterns 9, 11, 13, 12)—the liquid destroys the crystalline formations, and the system increasingly resembles a solution of the polymer in the plasticizer, as a result of which the temperature range of elasticity narrows.

Thus, X-ray structural analysis makes it possible to explain the elevated glass-transition temperature and flow temperature for plasticates with a low (2 wt.%) plasticizer content.

Figures 5 and 6 show curves of the dependence of \(\rho_v\) (volume resistivity) on temperature and of the current decay with time for the liquids studied. The curves were obtained on a galvanometric setup at \(U = 100\ \mathrm{V}\) by the direct-deflection method. 9-Octylcarbazole has a higher resistivity than DBC, especially at room temperature. This is partly explained by its higher viscosity in comparison with DBC. 3-Acetyl-9-octylcarbazole has a very low resistivity (about \(10^8\ \Omega \cdot \mathrm{cm}\) at \(100^\circ\mathrm{C}\)), which makes it unsuitable for use as a pri-

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Fig. 3. Dependence of viscosity on temperature for liquids (in centipoises): 1—DBS; 2—9-octylcarbazole; 3—3-acetyl-9-octylcarbazole.

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Fig. 4. X-ray diffraction patterns:
1—pure PVC;
2—PVC + 2 wt.% DBS;
3—PVC + 2 wt.% 9-OC;
4—PVC + 5 wt.% 9-OC;
5—PVC + 10 wt.% 9-OC;
6—PVC + 25 wt.% DBS;
7—PVC + 25 wt.% 9-OC;
8—PVC + 45 wt.% DBS;
9—PVC + 45 wt.% 9-OC;
10—PVC + 65 wt.% DBS;
11—PVC + 65 wt.% 9-OC;
12—PVC + 100 wt.% DBS;
13—PVC + 100 wt.% 9-OC.

![graph]

Fig. 5. Dependence of specific volume resistance on temperature for liquids: 1—DBS; 2—9-octylcarbazole; 3—3-acetyl-9-octylcarbazole.

as a plasticizer. Its low resistance is due to its greater polarity in comparison with 9-octylcarbazole, owing to the acetyl group. For the same reason, in 3-acetyl-9-octylcarbazole the current decreases with time more slowly (about 10 min) than in 9-octylcarbazole.

Fig. 5. Decrease of current with time for liquids: 1—9-octylcarbazole; 2—DBS; 3—3-acetyl-9-octylcarbazole.

Conclusions

1. The plasticizing action of 9-octyl- and 3-acetyl-9-octylcarbazoles on polyvinyl chloride was studied. The liquids studied cannot be used as plasticizers because of their poor compatibility with polyvinyl chloride and the insufficient frost resistance of plasticates based on these liquids.

2. X-ray structural analysis made it possible to reveal certain structural changes caused by plasticization.

Literature

1. T. I. Sokolova, G. L. Slonimskii. Journal of the All-Union Chemical Society named after D. I. Mendeleev, 6, 1961.

2. Kh. L. Gel'bchuk, V. I. Sedlis. ZhPKh, 30, 412, 1957.

3. K. Andrianov and D. Kardashev. Practical Work on Artificial Resins and Plastics. GKhI, 1946.

4. B. I. Iogin. Candidate’s dissertation. Novosibirsk, 1962.

5. E. I. Borg. Technology of Synthetic Plastics. GKhI, 1954.

6. A. I. Kitaigorodskii. Journal of the All-Union Chemical Society named after D. I. Mendeleev, 6, 1961.

7. V. A. Kargin et al. Koll. zh., 19, 142, 1957.