NOTES
248
MASS SPECTROMETRIC DATAA N D G-VALUES"FOR
Enerr. absorbed e.v. g X 1 0 - W
a
Vol. 62
TABLE^ I DECOMPOSITION GASESOF IRRADIATED POLYMER (Nz)
THE
Moles gas formed/mole monomer unit. 6'-values are given in parentheses HI hCN
Polyacrylonitrile 11.6 2 . 3 X lo-' (0.24) 4.0 X 29.0 9.0 x 10-4 (0.20) 8 . 0 X lod Polymethacrylonitrile ' 6.8 7.0 x 10-4 (1.0) 9 . 9 x 10-4 29.0 2 . 8 X IO-* (0.82) 3 . 0 x lo-* Number of gas molecules formed per 100 e.v. absorbed.
(0.041) (0.033) (1.4) (0.87)
CH4
0.0 0.0
3 . 2 X lo-' (0.44) 7 . 5 x 10-4 (0.22)
polymer, and only main chain breakage is noted a t fords 85% monomer when pyrolyzed,lB and its first. As irradiation proceeds, the availability of heat of polymerization may be estimated at about oxygen to the polymer molecules decreases; the 11-13 kcal./mole. It is seen that while the gross limiting intrinsic viscosity observed upon contin- irradiation results in nitrogen agree with the reued air irradiation indicates that cross-linking ported correlation, it does not seem possible at occurs concurrently. If PAN films 25 p thick are present to fully anticipate the effects of oxygen \ irradiated in air, almost no oxygen is available for in this process. radical combination and cross-linking to about the Acknowledgment.-The authors wish to thank same extent as when no oxygen was present is Mr. J. Neerman of the Physics Department for the observed. mass spectrometric data. Somewhat similarly, for powdered polystyrene (12) L. Tong and W. Kenyon, J . Am. Chem. Sac., 69,2245 (1945). sulfonate, a complete change over from cross(13) C. Schildknecht, ed., "Vinyl and Related Polymers," John linking in vacuo to degradation in oxygen is notedV3 Wiley and Sons, Inc., New York, N. Y., 1952, p. 290. Polymethacrylonitrile Powder.-In nitrogen and in air, chain degradation exclusively is observed HEAT OF FUSION, ENTROPY OF FUSION (Fig. 2); the oxygen effect is expIained by assuming AND CRYOSCOPIC CONSTANT OF T H E that the hindered radical species formed is stabilLiCI-KCl EUTECTIC MIXTURE1i2 ized by oxygen. It is interesting that while Wall and Brown4 found that the number of scissions BY C. SOLOMONS, J. GOODKIN, H. J. GARDNERAND G. J. JANZ produced by y-rays in polymethyl methacrylate decreased in air, Charlesby and his groupspB found Department of Chemistry, Rensselaer Polytechnic Inetitute, Troy, N . Y . the extent of main chain break in polymethyl Received September $4, 1967 methacrylate and polyisobutylene to be the same During the course of investigations in this Labofor irradiations in air, nitrogen or in vacuo. The role of oxygen in the high energy radiation of poly- ratory on the constitution of chloride melts containing titanium halides as solutes, an accurate mers has been discussed by other value of the heat of fusion of the LiC1-KCI eutectic Structure Changes.-It might be expected that mixture was required for the interpretation of the some branching would be noted, or the chain orien- results of cryoscopic measurements using this tation changed upon irradiation, but no significant solvent. The discrepancy between the best estidifferences were noted in the infrared spectra or in mated valuela kcal., mole-I, and an experithe X-ray diffraction patterns of the samples after mental value143.9 3.6 kcal. mole-', indicated a need exposure. A slight increase in C=C and C=O for further calorimetric studies. The present comabsorption was observed after air irradiation (50 X munication reports the values of the heat of fu1 0 6 rep.) of PMAN. I n addition, a small un- sion, entropy of fusion and cryoscopic constant identified peak appeared at 4.96 p for this system. of this solvent obtained in this Laboratory. Mass spectrometric analyses of the gaseous deExperimental composition products of the samples irradiated in The com osition of the LiCl-KCl eutectic mixture,6-B nitrogen are given in Table I; low molecular weight mole %%iCl, 42 mole % KCl, was checked cryoscopiunsaturates and nitriles were not observed, but a 58 cally in the present work. The cooling curves showed no small amount of methane from the a-methyl- discontinuities such as would be obtained if the. composition were other than the eutectic. The preparation of the substituted polymer was detected. mixture followed the recommendations described PAN produces no monomer when thermally eutectic elsewhere,DJo but with a molten salt filtration step introdegradedll and has a reported heat of polymeriza(1) Part I of a series of communications on the Constitution of tion of 17.3 kcal./mole;l2 PMAN, however, af(3) P. Alexander and D. Tome, ibid.,22, 313 (1956). (4) L. Wall and D. Brown, THIRJOURNAL, 61, 129 (1957). ( 5 ) P.Alexander, A. Charlesby and M. Ross, PTOC.Roy. Sac. London, A ~ S 392 , (1954). (0) P. Alexander, R. Black and A. Charleaby, ibid.. A2S%, 31 (1955). (7) L. Wall and M. Magat, J . chim. phys., 60,308 (1953). (8) A. Chapiro, ihid.. 63, 247 (1955). (9) P. Feng and J. Kennedy, J . Am. Chem. Soc.. 7'7, 847 (1955). (IO) N. Bach, "Proc. Int. Confer. Peaceful Uses Atomic Energy," Vol. 7, UNO, New York, N. Y., 1956, D. 538. (11) W. Burlant and J. Parsons, J . Polymer Sci., 22, 249 (1956).
Chloride Melts Containing Titanium Halides. (2) This work was supported by the Offioe of Naval Research, Metallurgy Branch, under Contract Nonr-591(06). (3) See discussion, this communication. (4) W. D. Powers and G. C. Blalock, Oak Ridge National Laboratory, Report No. CF-53-8-30, August 5, 1953. (5) W. Schaefer, 1. Mineral. Geol., I, 15 (1914). (6) H. Keitel, Neues. J . Mineral. Eeil. E d . , 52A, 378 (1925). (7) E. Elchardus and P. Lafitte, E d l . soc.chim., 61, 1572 (1932). (8) N,. 9. Dombrowskaja, J . Gen. Chem., U.S.S.R., 8 , 1007, 1017 (1933). (9) H. J. Gardner, C. T. Brown and G. J. Janz, THISJOVRNAL, 60, 1458 (1956).
NOTES
Feb., 1958
249
TABLE I HEATEVOLVED BY EUTECTIC IN COOLINQ FROM INITIAL TEMPERATURE TO 25'" Init. temp. eutectic
Temp. rise calorimeter,
("C.)
("C.)
Exptl. heat eq. calorimeter (cal. deg.-')
Exptl. heat evolved by eutectic and capsule (cal.)
Calcd. heat evolved by capsule (cal.)
Heat evolved by eutectia alone (cal. mole-1)
95.2 319.3 1.47 547.6 804.9 95.9 320.0 1.48 810.4 97.9 329.2 546.0 840.9 1.54 98.8 835.4 330.7 1.53 103.8 340.9 1.50 593.1 889.6 103.7 889.6 341.9 1.50 107.2 587.5 1556.8 358.5 2.65 109.0 361.7 2.69 1580.I 113.9 371.6 2.81 581.2 1633.1 113.5 372.6 1627.8 2.80 116.2 383.1 582.6 1683.7 2.89 Weight of sealed capsule plus eutectic, 21.014 g.; weight of
duced before the HC1 treatment to remove carbonaceous and other insolubles. The filtration apparatus was essentially a "Pyrex" glass tube with a sintered disc sealed in near the bottom. Standard taper ground glass joints at top and bottom were provided for admission of the solid and for the attachment of a receiver, respectively. A dripcone placed between the filter disc and the lower joint directed the filtrate vertically down the center of the tube so that contact of the molten salt with the joint did not occur. The apparatus, from just below the top cap to about 5 cm. below the drip-cone, was surrounded by a tubular furnace which maintained the temperature a t about 30" above the melting pointtof the salt. The filtrate, which a solidified in the receiver, was remelted and treated with dry HC1,lO the excess of the latter finally being removed by dry argon bubbling then prolonged evacuation. Samples of the eutectic prepared in this manner were found to have reproducible melting points of 354.3-354.4'. For the calorimetric experiments, weighed amounts of eutectic were sealed into capsules made from 10 ml. standard platinum crucibles in an atmosphere of pure dry argon to prevent hydrolysis, the lid of the capsule being sealed on with gold-palladium alloy solder. The calorimetric assembly, the technique used, and the "recording Beckmann thermometer" capable of measuring accurately and recording small changes of temperature of the order of 1-3", have been described elsewhere.lh12 Temperature differences were measured with an accuracy of fO.O1 O . Absolute temperatures were measured with an accuracy of f0.5', the limits being thoRe of the NBS calibration of the platinum/platinum-l00/, rhodium thermocouple used. Estimation of all the errors suggests that the measured heat of fusion is correct to within &27&
Results and Discussion The results of the calculations, including the corrections to bring all the temperature changes to 25", of heat content change are given in Table I. The final heat content change data are illustrated in Fig. 1. From these, a value of 3.20 f 0.06 kcal. mole-1 was obtained for the heat of fusion of the eutectic. A value of the heat of fusion may be estimated using the thermal data for the pure components assuming basic equation (1) applies AHe = XIAH?"
+ x2AHP + AHrn,
(1)
where AHe, AHlm, AHzm are the molar heats of fusion of the mixture and the pure constituents, respectively, a t the melting point of the mixture, T,. XI and are the mole fractions of the constitu(10) € A. I. Laitinen, W. 8. Ferguson and R. A. Osteryoung, J . Electrocham. Soc., 104, 616 (1957). (11) J. Goodkin, C. Solomons and G. J. Janz. Rev. Sci. Inst., in press. (12)C.Solomons and G. J. Janz, to he published.
Diff. final temp. from 25 a ("C.)
7.1 3641.5 5.6 3666.1 9.2 3812.3 8.1 3779.6 3.3 4031.8 4.6 4032.2 11.3 7437.7 9.3 7549.2 4.5 7795.0 6.9 7767.2 8042.6 7.8 eutectic alone, 10.895 g.
Cor. to heat evolved.by eutectic (cal. mole-1)
Cor.heat evolved by eutectic (cal. mole-')
83.1 65.5 107.6 94.8 38.6 53.8 132.2 108.8 52.7 80.7 91.3
3725 3731 3920 3874 4070 4086 7570 7658 7848 7848 8134
I
I
300
Fig. 1.-Heat
320 340 Tr 360 380 Initial temperature, ' C. content chan es as a function of temperature for the Lid-KCl eutectic.
ents. The basic Kirchhoff equation
was used to compute AHm from the heat of fusion, AHp, of the pure constituent at its melting point Tp. In equation 2, ACp = Cp(c)- CP(l)for the salts since the process is fusion rather than solidification. Using the values from the literature13 for LiC1: AHf (614O), 3.2 kcal. mole-'; Cp(s) = 11.00 3.40 X 10-3T, Cp(l) = 16.0; and for KC1: AHf (770°),6.4; Cp(s)= 9.89 5.20 X 10+T 0.77 X 10ST-2, Cp(l) = 16.0; a value of 3.9 0.3 kcal. mole-' for the LiC1-KC1 eutectic mixture is obtained, assuming, owing to the lack of data, that A H m i x is negligible. The large difference (16%) from the experimental value may be attributed in large part to sources of error inherent in the estimation procedure. A previous determination of the heat of fusion of the lithium chloride-potassium chloride eutectic mixture, by Powers and B l a l ~ c kgave , ~ a result of 64 cal. E.-' at 351", &.e.,3.6 kcal. mole-'. Recalculation from the original data4 was undertaken to check this value. The discrepancy can be resolved if the equations of Powers and Blalock are used, but with the last figure of each constant retained as significant for internal consistency. A value of 3.2 kcal. mole-', L e . , in good agreement with the result of the present measurements is thus obtained.
+
+
(13) K. K. Kelley, U. 8.Dept. Mines, Bull., 476, 1949.
+*
