NOTES
Jan., 1960 1 and 2, and thus the amount of oxygen formed during hydrolysis should be the same as the amount formed during thermal decomposition. 2Na03 +2Na02 + + 2Hz0 +2NaOH + H2O2+ O2 0 2
2NaOz
(1) (2)
The values found were 6.1 and 5.9 cc. during hydrolysis, compared to 2.0 and 2.5 cc. during decomposition of the ozonized sample. This indicates that considerable amounts of the superoxide are also formed at -60', although the results can also be attributed to t,he presence of some unextracted ozonide. We have confirmed the fact that diffuse reflectance measurements on the sodium ozonide formed at 25" show a broad peak a t approximately 450 mp, although no ozonide can be extracted. We also have found that the decomposed bed from the preparation a t - 60' gives the same absorption. One possible explanation for this and the results of McLachlan, et al., is that a small amount of sodium ozonide is trapped in the sodium hydroxide and thus stabilized toward thermal decomposition. Since sodium hydroxide is not soluble in liquid ammonia, the trapped material would not be extracted. Another possibility is that sodium ozonide exists in two forms, one being soluble in liquid ammonia and unstable a t room temperature, and the other being insoluble and stable. However, it does not appear that the ozonides formed a t the two different temperatures are chemically different, since their spectra are identical. The idea of two crystalline structures of ozonides is not unfounded, in that we have observed that potassium ozonide may exist in two forms. Zhdanov and ZvonkovaG have found potassium ozonide to have the tetragonal potassium bifluoride lattice of potassium azide. However, we have found that potassium ozonide may also exist in the monoclinic potassium nitrite structure. These results have also been predicted by Smith.' Currently, we are investigating all of these possibilities. (6) G. S. Zhdanov and Z. V. Zvonkova, Zhur. F w . Khzm., 26, 100 (1951).
(7) P. Smith, THISJOURNAL. 60, 1471 (1956).
SPHERULITE GROWTH RATES IN POLYETHYLEKE CROSSLINKED WITH HIGH ENERGY ELECTRONS BY FRASER P. PRICE Contribution from the Research Laboratory of the General Electric Cam pony, Schenectady, New York Received J u l y $0,1969
It is known that when polyethylene is crosslinked by ionizing radiation a t temperatures above the crystal melting point, the equilibrium degree of crystallinity below the melting point is reduced. Also the size and perfection of the crystallites comprising this crystallinity is reduced.2 In view of these facts it is worth inquiring about the effects of irradiation upon the growth of spherulites. This (1) A. Charleaby and L. Callaghan, J . Phys. Chem. Solids, 4, 306 (1958). (2) L. Mandelkern, D. E. Roberta, J. C. Halpin and F. P. Price, J . Am. Chem. Soc.. 83, in press (1960).
169
note reports the results of some studies of the growth rates of spherulites growing from crosslinked melts. Since a photographic technique, which relied upon the birefringence of the growing spherulite, was used and since there is a persistence of birefringence in the melts of polyethylene irradiated when cry~talline,~.3 this study is only concerned with spherulite growth from melts of polyethylene that was irradiated when molten. Experimental The polyethylene was Marlex 50 obtained from the Phillips Petroleum Co., Bartlesde, Oklahoma. Pressed sheets about 1 mil thick supported on microscope cover slips were irradiated at 150' in an atmosphere of nitrogen with 800 KV peak electrons. The electrons were supplied by a G.E. resonant transformer type electron generator. Spherulite growth rates were measured using the polarizing microscope and photographic techniques. A special hot stage consisting of two insulated brass blocks was constructed. These blocks were mounted side by side about one quarter inch apart and were heated electrically. One block, the melting block, was held at some temperature TIabove the melting temperature to *lo by adjusting the heat input to the requisite value. The other block, the gro5ng block, was held a t some temperature T2 below the melting point to f O . l O by a thermocouple controlled relay system which actuated the heater. The growing block had a small hole bored through it to permit the use of transmitted light. I n order to minimize temperature variations from stray air currents, a small brass cup with an appropriately placed glass-covered viewing hole was inverted over the specimen when observations were being made. The temperature of the growing block was determined by a thermocouple located in the block close to the central hole. Benzoic acid, U.S.Bur. of Std. calorimetric grade, was used to calibrate the thermocouple. The procedure in making a run wm as follows: place 1 mil sample between cover slips on the melting blork a t Ti; after 10 min. place brass cup, which was at T2, over specimen and slide it over the hole in the growing blork; focus microscope and take photomicrographs at appropriate intervals. Kodak Plus X film was used in a h i c a camera fitted to the microscope with a Mikas photomicrographic ad?pter. The negatives were projected on a screen and the diameters of selected spherulites were determined as functions of time. Plots of diameter versus time were good straight lines. The growing block also was used to determine crystal melting points. In these determinations the tem rature was raised at O.l'/min. and the temperature at wFch the last observable crystals disappeared wm taken as the melting point.
Results and Discussion The results of this study are presented in Table I. The data show that growth rates can be determined to +5% (cf. runs at 100 MR, T2 = 100.0"). It can also be seen that changing !PI does not alter the growth rate (cf. runs at no dose, Tz = 122.5122.9'). As has been determined for other polym e r ~the~ growth rate is determined primarily by the growth temperature Tz. Each set of data at a particular dose shows that there is a temperature range in which the growth rate is extremely sensitive to temperature. This effect has been observed in other polymers by other investigator^^^^ and has been attributed to an enhanced nucleation rate immediately ahead of the advancing spherulite boundary. The results given in the table show that as the dose is increased the temperature at which compar(3) C. F. Hammer, W. W. Brandt and W. L. Peticolas, J . Polymer
So., 84. 291 (1957). (4) F. P. Price, J . Am. Chem. Soc., 74, a l l (1952). ~ 18. 592 (195s). (5) P. J. Flow and A. D. Mclntyre, J . P d u m Sei., (6) F. P. Price in "Growth and Perfection of Crystals." John Wiley and tions, New York, N. Y., 1958, p. 533.
NOTES
170
1701. 64
TABLE I the crystal melting point. -4s noted above this is consistent with the concept of nucleation control SPHERULITE GROWTH RATESIN IRRADIATED POLYETHYLENE Ti
TI
Diametral growth rate (mm./min.
x
("C.)
("C.1
191 192 193 196 168 153
Dose = 0 MR. 120.7 122.9 125.1 127.0 122.4 122.5
1.34 1.24 0.218 0,013 1.06 1.21
195 195 195
Dose = 20 MR. 114.0 116.4 118.6
1.21 2.59 0.51
195 195 195 195 195 195
Dose = 40 MR. 113.1 113.8 114.6 115.8 117.0 117.8
3.5 2.7 2.6 0.79 .54 .028
195 195 195 195
Dose = 100 MR. 100.0 100.0 101.8 104.0
.87 .74 .39 ,095
of spherulite growth.
102)
SURFACE TENSION, IKTERMOLECULSR DISTANCE AND INTERMOLECULAR SSSOCIATION EXERGY OF PURE NOK-POLAR LIQUIDS 1 BY RALPHG. STEINHARDT, .JR. Deportment o f ChemistlrJ, Hollins College, V
