The dielectric properties of Ices II, III, V, and VI have been measured up to 300 kc/sec over a range of temperatures and pressures. All except Ice II exhibited well-defined dielectric dispersion and so are orientationally disordered under the experimental conditions. The dispersion loci were slightly broader than Debye curves, which may reflect the presence of nonequivalent crystal sites. As for Ice I, the static dielectric constants correspond to values of about 3 for the Kirkwood orientational correlation factor. This suggests that these forms of ice are four coordinated, in agreement with infrared and (for Ice III) x-ray evidence at low temperatures. The relaxation rates are considerably faster than for Ice I, and the activation energies and entropies somewhat lower. The volumes of activation are all about 4.6 cm' mole-i. The relaxation mechanism appears to be similar to that in Ice I, i.e., relaxation occurs by diffusion of orientational defects.X-ray and infrared studies have indicated that Ice II is rotationally ordered near liquid-nitrogen temperature. The absence of orientational polarization in Ice II at temperatures as high as -30 0 shows it to be ordered throughout its region of stability.

The phase diagram of the acetone-water system sholvs that acetone hydrate dgcomposes a t an incongruent melting point. The existence of acetone hydrate is confirmed b~-a study of thc low-frequency dielectric properties of this system. A dispersion region, related to the relaxation of water tnolecules in the clathrate structure, is characterized by a "static" dielectric constant and an activation energy about half as large as the corresponding values for ice, and by a limiting high-frequency dielectric constant of about 'i a t 200' K. The magnitude of the latter is attributed to orientation of acetoile n~olecules within the larger ca\ ities of the hydrate structure.I t is now well-established that a cubic form of ice which is stable a t low temperatures for long periods of time can be formed by condensation of water vapor on a sufficiei~tly cold surface (I). Since 1896 several workers have reported that an isotropic form of ice could be formed by cooling aqueous solutions of a large number of organic substances, including acetone (for surnmary, see ref.2 ) . In particular, Cohen and van der Horst (3) suggested the formation of "ice VIII" in cooled concentrated solutio~ls of acetone and other organic liquids. They inferred that acetone was found in their a n a l~s e s of the crystals as a result of their inability to separate the crystals completely from the acetonerich mother liquor. Recently an X-ray study by Quist and Frank (4) clearly suggested t h a t the cubic solid obtained a t high acetone concentrations was acetone hydrate rather than ice VIII. The diffraction patterns were identical with those reported by von Stackelberg and hliiller (5) for "hydrates of structure 11" like those of CHC13 and C2H6C1. In these structures, first proposed by Claussen (6), the organic molecules (A) occupy the larger of two different-sized cavities formed by a lattice of hydrogen-bonded water molecules. Since there are eight large cavities to the 136 water molecules in the unit cell, the maximuin A content is given by A . 17H20. The oxygen atoms of the water n~~l e c u l e s belong to space group Oh7-Fd3m and theside of the unit cell is 17.2 A.In view of the uncertainty of the co~lditio~ls of existence of acetone hydrate arid our interest in molecular motions in clathrate structures of this type, we have studied the acetone-water system a t low temperatures by means of low-frequency dielectric measurements, as well as by thermal analysis. EXPERIMENTAL I\/IETHODSDielectric measurements were made on solutions of four concentrations (15.5, 27.0, 27.5, and 97.7 wt%) of distilled Reagent Grade acetone (conductivity l.2X10-7 ohm-lcm-l) in conducti~ity water. Temperatures were between -194 and -15" and frequencies between 0.050 and 500 kc/sec, uith instrumentation as previously indicated (7, 8 ) . The cell was a three-terminal type with vertical coaxial stainless steel electrodes. Samples of known composition slowly frozen in this type of cell were found in the course of preliminary work on other hydrates (9) to be as satisf...

The static dielectric constant of liquid ethylene oxide has been measured between 158 and 286 °K. The hydrate of ethylene oxide exhibits a dispersion–absorption region characterized by static dielectric constants about one-third as large as those of ice and by relatively large "high-frequency" dielectric constants (ε1 = 7.5 at 0 °C). This region may be approximately described as a circular arc locus, but may be represented somewhat better by a superposition of two (or three) semicircular dispersions. In either case, the activation energy for the relaxation of water molecules, to which this region is ascribed, is ca. 6.7 kcal/mole, except at low temperatures, where it becomes smaller. Experimental values of ε1 agree roughly with those calculated for comparatively rapid orientation of ethylene oxide molecules in the cavities of the hydrate. Such orientation may account for absorption maxima observed at 11 Mc/sec and above 100 Mc/sec at 90 °K.

The reactions of peroxides with polymers have been studied for some time. They form an extensive part of vulcanization technology. Two types of reactions are generally recognized, those leading to crosslinking between polymer chains and those leading to scission of the chains. Natural rubber, polybutadiene and ethylene-propylene rubber are examples of polymers in which crosslinking reactions take place to a greater extent than reactions leading to chain scission and these polymer reactions with peroxides form a useful method of vulcanization. On the other hand, polyisobutene is an example of a polymer which degrades extensively and for polyisobutene and butyl rubber, peroxides have not found use as cross-linking agents.

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