June, 1962
1201
NOTES
TABLE I CALCULATED HEA'I' O F FORMATION O F DIFLUOROSILYLENE
T("K.)
System
- R In
Equilibrium pressure bm.) SiFl
SiFza
50 45 5 5 2.5 2.5 I500 50 45 5 2.5 2.5 5 1.8 1.2 3 45 5 1GO0 50 5 2.5 2.5 a Estimated from yields of polymerized products.
14.3 11.4 14.3 11.4 13.6 14.3 11.4
1400
A
( 9 ) -
oal. deg. -1 mole-'
(koal./mole)
A.HiO[RiFr(g)] (kcal./mole)
46.96 46.96 46.75 46.75 46.75 46.54 46.54
85.8 81.6 91.6 87.2 90.6 97.4 92.6
150.1 152.2 148.2 149.5 147.8 144.3 146.75
AHP88.16
_ .
SiFI (-386 kcal. mole-') as determined by Rise, et ~ 1 . ~using 8 the direct reaction of silicoii and fluorine. (8) S. S. Kise, 1%'. N. Hubbard and J. L. Margrave, Argonne National Laboratory Report KO.0472, January, 1902.
mersed in the melt contained in a molybdenum cup. The apparatus, experimental procedure, and determination of the cell constant are described elsewhere.2~3 A sapphire capillary cells was used to confirm the previously established conductivity of Cd-CdClz solutionslo which served as standards to determine the cell constant of the parallel electrode a~sembly.2,~Further imeasurements of the cell constant established its value with a precision of 3~1%. The synthetic sapphire cell was used to measure the conductivity of the uure PrCla. The PrCL was repared from the oxide in the same manner as LaCla and Nd8lB.a
THE ELECTRICAL CONDUCTIVITY OF SOLTiTIOSS OF METALS IN THEIR MOLTEN HALIDES. V. Results and Discussion PRASEODY~~IUJI-PRBSEODYMIUM The specific conductivity, K (ohms-1 crn.-l), for TRICHLORIDE' PrC13is given by the equation BY A. S DWORKIN, H.R. BRoixsi3EIN, AND hf. A. BREDIG KP~CI~
Chemzstry Dnaszon, Oak Radge 'Vafaoval Laboratory, Oak Rzdoe, Tennessee Rcceibed 2Vauember f 4 , 1961
-.1.189 4- 2.75 X 10-at
over the temperature range measured, 800-860". These values and those for LaClSJ3CeC13,2and KdThe rapid increase in the electrical conductivity c133 form a regular series of K us. t curves where K with metal concentration in solutions of Ce in decreases with increasing atomic number or deindicates a large pro- creasing size of the cation. CeC132 and of La, in portion of conductance by electrons in the satuConductivities of LaCL, PrC13, and NdC& rerated solutions. In solutions of Xd in XdCP3,3 ported by Voight and Biltzll are considerably on the other hand, a very small increase in con- lower than ours. [n subsequent papers, Biltz, ductivity indicates very little or no electronic et uZ.,12 rejected the earlier values as being too low conductance. These results reflect the large, due to polarization. From repeated measurements systematic differences in the phase diagrams: no on LaCL, corrections were estimated for the resolid phasc containing Ce or La in a valence state maining salts. However, their final values, still lon-er than three n'as found in the Ce-CeCL4 about 10% lower than ours, were obtained a t only or La-La(W systems, whereas in the IYd-IYdCl, one, fairly low frequency, 500 cycles, so that it system an electrically insulating solid, NdC12, as still is doubtful whether polarization was comwell as XdCh 27 and SdC12.,37, exists.6 The present pletely eliminated. This, together with other report deals with the Pr-PrC13 system, which is possible effects such as purity of materials and intermediate in that the phase diagram shows no bubble formation on the electrodes,12amay account solid I'rCls, but only the mixed chloride P I - C I ~ . ~for their low results. stable in Ihe rather small temperature range beTable I lists the specific conductivity of I'rtn-een 590 and G 5 9 1 O . 7 PrC13 solutions a t 830" up to a compositioii near saturation. A short extrapolation of the I'rEiperimental PrC13 conductivities obtained with the parallel Thr reactivitv of the solutions with ceramic materials8 necessitated thr u-e of a conductivity apparatus in which two electrode cell to that of pure PrC13yields a specific rigidly moui ked parallel dectrodes of molybdenum were 1m- conductivity in excellent agreement with the valuc determined by means of the sapphire cell. (1) Work performed for the C . S. Atomic Energy Commission a t the The accelerated increase in conductivity with Oak Ridge N,tltional h h o r a t o r y , oriernted b y the Union Carbide metal concentration in the La and Ce solutions Corporation. Oak Ridge, Trnnrsaee. ( 2 ) H. R. Hronst>ein, A . 8 . Dwurkin. and PI. A . Nredig, .I. P h y s . has been attributed293 to increasing orbital overlap Clism., 66, 41 (lQ62). and gradual establishment of a conduction band (:I) A. S. I l n o r k i n , T1. R . 13ronslein, a n d &I. A. I3rediK. Diurunsions -.
I ~ a , a d a ySoc., i n p w w . (4) 0. &lellors a n d S. Senderoff. J . I'kus. Chem.. 63. 1111 i,l 9 B R ) .. ( 5 ) I;. J. Keneshea a n d D. Cubicciotti, J. Chem. E ~ QD.a t a , 6, 507 (1961). (6) L. F. Druding a n d J. D . Corbett, J . Am. Chem. Sac., 83, 2462
w.
.
I
~
(le6l).
(7) L. I:. Driiding a n d J. D. Corbett. t o be published. (8) H. R . Bronstein, A. S. Dworkin, and M. A. Bredig, J. Phys. Chem., 6 4 , 1344 (1960).
(9)
IT. K. Bronstein and &I. A. Eredip, 1.A m . Cirsm. Soc.,
80, 2077
(195X).
(10) (a) A. IT. W. Aten, Z. phgsik. Chem., 78, 578 (1910); (b) C. A. Angel1 and J. W. Tomlinson, Discussions Faradall SOC.,in press. (11) A. Voight a n d W. Biltz, Z. anorg. U. allgem. Chem., 183, 277 (1924). (12) (a) W. Biltz a n d W. Klemm, Z. p h v s i k . Citem., 110,318 11924); (b) W. Klemm and IT. Biltz, Z . anorg. u . allgem. Ciiem., 152, 231 (1928).
so7 'ES
1202
8
r
1'01. 66
j
ISTERMOLECULAR ENERGY TRANSFER I N POLYETHYLENE-POLYBUTADIENE BLENDS DURING */-IRRADIATIOI$ BY MORTOX A. GOLUB StanfoTd Research Institute, M e d a Park, CalCfovn~a Recezved December 16, 1961
i
Although intramolecular transfer of excitational and/or ionizational energy in high polymers is well known and accounts, for example, for the pronounced radiation resistance of polystyrene com'E .c 0 pared to polyethylene, few instances of intermoY lecular energy transfer between different polymer molecules have been reported. Recently, Dole and Williarns*.2found that in the yirradiation of a polyethylene-cis-polybutadiene blend at 142' the polyethylene was protected to some extent against decay of vinyl groups and evolution of hydrogen while the polybutadiene underwent cis-trans isomerization. An even greater I I I I I I I I protective effect was imparted to polyethylene by 0 4 0 (2 16 20 24 28 trans-polybutadiene but no isomerization of this MOLE %METAL IN MCI, . polymer was detected, presumably because the radiostationary equilibrium is far over on the trans Fig. 1.-Specific conductivity of M-PIICL solutions. side3 and what cis units would be formed would be difficult to detect by infrared spectroscopy since their absorption coefficient is about oneTABLEI fourth that of the corresponding trans units. Practically no protection or isomerization effects SPECIFICCONDUCTIVITY OF SOLUTIOKS OF PRASEODYMIUM were observed in the room temperature irradiaIN MOLTEN PRASEODYMIUM TRICHLORIDE AT 830" tion of polyethylene-polybutadiene blends, apMole % Pr x(ohm-' cm.-l) parently because of the non-homogeneous nature 0 1 09 (sapphire cell value) of the mixtures, which inhibits energy transfer from 0 I . 10 (extrapolated, parallel crystalline polyethylene to amorphous polybutaelectrode cell) diene. These results are analogous to those ob1.1 1.20 tained by Witt4 indicating no intermolecular energy 3.2 1.39 transfer from polybutadiene to polystyrene in 6 0 1.68 physical mixtures of these two polymers but con10.6 2.22 siderable intramolecular energy transfer from the 15.3 2.90 butadiene to the styrene segments in corresponding 17.8 3.37 copolymers. Evidently, the physical mixtures of polybutadiene and polystyrene likewise were not sufficiently homogeneous to permit a significant for electrons from M + M 3 + 3e. These mobile amount of intermolecular energy transfer. Conelectrons may be in equilibrium (&I3* e- = ceivably, a more intimate mixture of these polymers W+) with divalent metal ions known to exist in would show such transfer but this has not been other rare earth ~ystems.6.l~Conductivity meas- achieved. urements in the Sd-XdCls systemj3 where the An estimate by this author3 of the G-value for stable insulating solid NdClz is known, strongly isomerization of 5% cis-polybutadiene (CPB) in indicate that the Nd2f is not dissociated into S d 3 + polyethylene (Pa)a t 142' gave a yield (based on e-, Figure 1 shows the electrical behayior of the energy absorbed directly by CPB) of about four Pr metal dissolved in molten PrC13 to be interme- times that in the pure CPB. This result! coupled diatr between La and Ce on the one hand and S d with the observed protection in PE indicated thr on thr other, but much closer to the latter. This likely occurrence of intermolecular enrrgy transfer beharior can be explained in terms of a PrZc ion in the PE-CPB blends. In fact, Dole and Wilattributed the reduction in hydrogen rvoluwhose stability in the melt is considerably greater liams1j2 tion to charge transfer, and the reduction in vinyl than that of the relatively unstable La2+and Ce2f decay to transfer of excitation energy from the ions and close to that of stable Nd2f ion. The methylene groups in PE to the vinylene units in upward curvature of the specific conductance vs. polybutadiene. The latter groups thus were conconcentration curve (Fig. 1) for Pr-PrC4 can be (1) BI, Dole and T. F. Williams, Discussions Faraday Sac., 27, 74 attributed to the gradual overlap of the orbitals of (1959). the conduction electrons as discussed previously.3 (2) T. r. W ~ l l ~ a masn d BI Dole. .I A m . Chem S o c , 81, 2919
-
1
+
+
+
(13) J. D. Coibett, L. F. Driiding, T. L. Riiikhard, a n d C . I ~ u t t ~ lD~~ lv,e ? i . m o n sF ' u T ~ IS n~ c , in prew
n.
(1959). (3) 11 A. Golnh, zbzd , 82, 3097 (1960); cf f o o t n o t r *5 ( 4 ) E a i l i ,I. P o l y m e r SLL.,41, i07 (lc131)
