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Solubility of mesophase pitch
Letters to the Editor where [Cl, [Ml and jM+] represent the concen~ations of catalyst C, monomer M and propagating polymeric cation &f+, respectively. If the steady state where the initiation rate r, is equal to the termination rate r, is assumed, a constant concentration of M’ is given by
tM+l = ~~[Cl[~l/~*[CBl. so that the polymerization rate Rp is defined as follows:
0
2
1
‘/[c.
3
4
81 I s’
Fig. 3. Dependence of polymerization rate on the amount of carbon black. Five grams of styrene were polymerized in the presence of Philblaek 0 at 0°C using stannic chloride (8.3 x low4mol) in a solvent consisting of nitrobenzene (30ml) and carbon tetrachloride (28 ml).
Since this equation is consistent with the result shown in Fig. 3, it is reasonable to assume that the termination reaction occurrs on the surface of carbon black. The reaction sites on carbon black surface and the mechanism of grafting are being investigated in detail. Faculty of Engineering Niigata University Ga~o-cho l-2, ~ag~o~a Japan
(940)
KUMAKAZUOHKITA MASATO SHIMOMURA TERUYUKITSUHTA
REFERENCES
with the rate
I. K. Ohkita, N. Tsubokawa. M. Noda and M. Uchiyama, Carbon 15, 194(1977). 2. E. Papirer, J. C. Morawski and A. Vidal, Ang. Makromol, Chem. 42,91 (1975). 3. K. Ohkita, N. Tsubokawa, E. Saitoh, M. Noda and N. Takashina, Carbon 13,443 (1975). 4. J. W. Breitenbach and H. Preussler, J. Pdymer SC?. 4, 751 (1949). 5. G. Kraus, J. T. Gruver and K. W. Rollmann, J. Polymer Sci. 36, 564 (1959). 6. J. B. Donnet and G. Henrich, 1. Polymer Sci. 46,277 (1960).
rp = k,IMJ[M’]. Termination: M,+ + CB +
&
unreactive species
with the rate r, = k,[M+l[CB]
Solubiity of mesophasepitch (Received 4 November 1977) It is now well recognized that pitch is gradually transformed to a mesophase state during carbonization. The kinetics of mesophase formation has been correlated with the quality of mesophase and hence of the derived carbon. The anisotropic phase in mesophase pitch can be observed directly with the aid of a polarizing microscope, but it has become customary to monitor the extent of mesophase formation by measuring the change in solubility. The amount of insolubles in excellent pitch solvents, such as quinoline, pyridine, and anthracene oil has been equated to the mesophase content, and this relation has been adequate for mesophase pitches prepared by simple heat-treatment [l-8]. However, we wish to show in this communication that solubility cannot be used universally as a criterion for the amount of mesophase. The solubility of a particular mesophase pitch is related to the nature of the precursor, the mesophase prep~ation procedure, and to the specific solvent employed. Mesophase contents and solubility data were determined for mesophase pitches prepared with varying amounts of mesophase. The amount of mesophase was controlled by heat-treating for various periods of time at a fixed reaction tem~rature while sparging by bubbling inert gas through molten pitch to remove the volatiles. The mesophase content was computed by estimating the fraction of the area consisting of anisotropic phase in a vertical polished section of an entire sample of the pitch, Solubility data were determined in pyridine, toluene, and quinoline. The solubilities in pyridine and toluene were obtained by an exhaustive Soxhlet extraction of finely crushed pitch at the
boiling point of the respective solvents. The quinoline solubility was obtained by refluxing 0.5 g of pitch with 180ml of quinoline for 30 min and then filtering and weighing the insolubles. In Fig. 1, the percent of mesophase is plotted vs the per cent of pyridine insolubles for mesophase pitches made from two different precursors. Precursor A is a petroleum-derived pitch which forms large anisotropic mesophase domains while precursor B is an ethylene tar pitch which forms a more disordered carbon structure and gives a stringy coalesced and small-domain mesophase. A dotted line indicating the situation in which the percentage of insolubles would equal the mesophase content is also drawn on Fig. 1. It is apparent for both precursors that the amount of mesophase does become greater as the percentage of insolubles increases. However, there is not an exact correspondence between the amount of mesaphase and the insoluble content. For precursor B, the amount of insolubles is greater than the mesophase content up to about 75% PI, while for precursor A, the mesophase content is generally considerably higher than the amount of insolubles, The solubilities of pitches with different mesophase contents prepared from precursor A are shown in Fig. 2 for three solvents, quinoline, pyridine and toluene. The solubility is always highest in quinoline and lowest in toluene. The dotted line in Fig. 2 shows the relationship expected if the isotropic phase were totally soluble and the anisotropic phase were totally insoluble. The experimental data do not follow this line with any of the three solvents. Tofuene, the poorest solvent, does not even
Letters to the Editor
1.51
dissolve all of the isotropic phase in pitches containing less than 60% mesophase, while pyridine and quinoline must dissolve appreciable amounts of the anisotropic phase in addition to the isotropic phase. It is interesting that some of the anisotropic phase must dissolve even in toluene as seen from the solubility of pitches with mesophase contents greater than 60%. in conclusion. it can be stated that the amount of mesophase IS not necessarily equal to the amount of insolubles in pitch formed by heat-treatment. The mesophase can include both high molecular weight components which are insoluble, and lower molecular weight species which are soluble. For determining the mesophase content in pitch. one must rely on optical microscopy methods and not on solubility criteria. 0
20
40 60 PYRIDINE iNS~UBLE(‘~)
Fig. 1.
MESOPHASE (%)
Fig. 2.
80
loo
Union Carbide coloration Carbon Products Division Patma Technical Center Parma, OH 44103, US A.
S. CHWASTIAK
I. c. LEWIS
1. J. D. Brooks and G. H. Taylor, Nature 206,697 (1965) 2. P. Chtche. J. Dedutt and F. Ftscher. J. Chem Phv.~. 66, 28 (1%9). 3. H. Honda, H. Ktmuara, Y. Sanada, L. Sugawara and T. Futura, Carbon 8, 181(1970). 4. M. P. Whittaker and L. I. Grindstaff, Carbon 10, 165 (1972). 5. K. J. Huttinger. Erdol und Kohle 26,21 (1973). 6. H. Tillmanns and 0. Pietzka. Deatsche Keramische Geselischajt, Carbaa 76. Preprints of 2nd International Carbon Conf., Baden-Baden, p. 39 (1976). 7. S. Oi, T. Imamura, M. Kamatsu, Y. Yamada, M. Nakamizo and H. Honda. Extended Abstracts of 13th Biennial Carbon Conference. Irvine, California, p. 310.American Carbon Society (1977). 8. I. Mochida, K. Maeda and K. Takeshita, Carbon 15. 17 (1977).
tM+l = ~~[Cl[~l/~*[CBl. so that the polymerization rate Rp is defined as follows:
0
2
1
‘/[c.
3
4
81 I s’
Fig. 3. Dependence of polymerization rate on the amount of carbon black. Five grams of styrene were polymerized in the presence of Philblaek 0 at 0°C using stannic chloride (8.3 x low4mol) in a solvent consisting of nitrobenzene (30ml) and carbon tetrachloride (28 ml).
Since this equation is consistent with the result shown in Fig. 3, it is reasonable to assume that the termination reaction occurrs on the surface of carbon black. The reaction sites on carbon black surface and the mechanism of grafting are being investigated in detail. Faculty of Engineering Niigata University Ga~o-cho l-2, ~ag~o~a Japan
(940)
KUMAKAZUOHKITA MASATO SHIMOMURA TERUYUKITSUHTA
REFERENCES
with the rate
I. K. Ohkita, N. Tsubokawa. M. Noda and M. Uchiyama, Carbon 15, 194(1977). 2. E. Papirer, J. C. Morawski and A. Vidal, Ang. Makromol, Chem. 42,91 (1975). 3. K. Ohkita, N. Tsubokawa, E. Saitoh, M. Noda and N. Takashina, Carbon 13,443 (1975). 4. J. W. Breitenbach and H. Preussler, J. Pdymer SC?. 4, 751 (1949). 5. G. Kraus, J. T. Gruver and K. W. Rollmann, J. Polymer Sci. 36, 564 (1959). 6. J. B. Donnet and G. Henrich, 1. Polymer Sci. 46,277 (1960).
rp = k,IMJ[M’]. Termination: M,+ + CB +
&
unreactive species
with the rate r, = k,[M+l[CB]
Solubiity of mesophasepitch (Received 4 November 1977) It is now well recognized that pitch is gradually transformed to a mesophase state during carbonization. The kinetics of mesophase formation has been correlated with the quality of mesophase and hence of the derived carbon. The anisotropic phase in mesophase pitch can be observed directly with the aid of a polarizing microscope, but it has become customary to monitor the extent of mesophase formation by measuring the change in solubility. The amount of insolubles in excellent pitch solvents, such as quinoline, pyridine, and anthracene oil has been equated to the mesophase content, and this relation has been adequate for mesophase pitches prepared by simple heat-treatment [l-8]. However, we wish to show in this communication that solubility cannot be used universally as a criterion for the amount of mesophase. The solubility of a particular mesophase pitch is related to the nature of the precursor, the mesophase prep~ation procedure, and to the specific solvent employed. Mesophase contents and solubility data were determined for mesophase pitches prepared with varying amounts of mesophase. The amount of mesophase was controlled by heat-treating for various periods of time at a fixed reaction tem~rature while sparging by bubbling inert gas through molten pitch to remove the volatiles. The mesophase content was computed by estimating the fraction of the area consisting of anisotropic phase in a vertical polished section of an entire sample of the pitch, Solubility data were determined in pyridine, toluene, and quinoline. The solubilities in pyridine and toluene were obtained by an exhaustive Soxhlet extraction of finely crushed pitch at the
boiling point of the respective solvents. The quinoline solubility was obtained by refluxing 0.5 g of pitch with 180ml of quinoline for 30 min and then filtering and weighing the insolubles. In Fig. 1, the percent of mesophase is plotted vs the per cent of pyridine insolubles for mesophase pitches made from two different precursors. Precursor A is a petroleum-derived pitch which forms large anisotropic mesophase domains while precursor B is an ethylene tar pitch which forms a more disordered carbon structure and gives a stringy coalesced and small-domain mesophase. A dotted line indicating the situation in which the percentage of insolubles would equal the mesophase content is also drawn on Fig. 1. It is apparent for both precursors that the amount of mesophase does become greater as the percentage of insolubles increases. However, there is not an exact correspondence between the amount of mesaphase and the insoluble content. For precursor B, the amount of insolubles is greater than the mesophase content up to about 75% PI, while for precursor A, the mesophase content is generally considerably higher than the amount of insolubles, The solubilities of pitches with different mesophase contents prepared from precursor A are shown in Fig. 2 for three solvents, quinoline, pyridine and toluene. The solubility is always highest in quinoline and lowest in toluene. The dotted line in Fig. 2 shows the relationship expected if the isotropic phase were totally soluble and the anisotropic phase were totally insoluble. The experimental data do not follow this line with any of the three solvents. Tofuene, the poorest solvent, does not even
Letters to the Editor
1.51
dissolve all of the isotropic phase in pitches containing less than 60% mesophase, while pyridine and quinoline must dissolve appreciable amounts of the anisotropic phase in addition to the isotropic phase. It is interesting that some of the anisotropic phase must dissolve even in toluene as seen from the solubility of pitches with mesophase contents greater than 60%. in conclusion. it can be stated that the amount of mesophase IS not necessarily equal to the amount of insolubles in pitch formed by heat-treatment. The mesophase can include both high molecular weight components which are insoluble, and lower molecular weight species which are soluble. For determining the mesophase content in pitch. one must rely on optical microscopy methods and not on solubility criteria. 0
20
40 60 PYRIDINE iNS~UBLE(‘~)
Fig. 1.
MESOPHASE (%)
Fig. 2.
80
loo
Union Carbide coloration Carbon Products Division Patma Technical Center Parma, OH 44103, US A.
S. CHWASTIAK
I. c. LEWIS
1. J. D. Brooks and G. H. Taylor, Nature 206,697 (1965) 2. P. Chtche. J. Dedutt and F. Ftscher. J. Chem Phv.~. 66, 28 (1%9). 3. H. Honda, H. Ktmuara, Y. Sanada, L. Sugawara and T. Futura, Carbon 8, 181(1970). 4. M. P. Whittaker and L. I. Grindstaff, Carbon 10, 165 (1972). 5. K. J. Huttinger. Erdol und Kohle 26,21 (1973). 6. H. Tillmanns and 0. Pietzka. Deatsche Keramische Geselischajt, Carbaa 76. Preprints of 2nd International Carbon Conf., Baden-Baden, p. 39 (1976). 7. S. Oi, T. Imamura, M. Kamatsu, Y. Yamada, M. Nakamizo and H. Honda. Extended Abstracts of 13th Biennial Carbon Conference. Irvine, California, p. 310.American Carbon Society (1977). 8. I. Mochida, K. Maeda and K. Takeshita, Carbon 15. 17 (1977).