The low electrical resistance of vulcanizates loaded with conductive carbon blacks in a given particle size range is cause by the low density of the particles, high structure, or both. In addition, the smaller the particle size of the black, the lower the resistivity. The same factors also cause high modulus and, in liquid dispersions, high viscosity. It is shown that acetylene black owes its lower resistivity in vulcanizates to its high structure. Vulcan XC 72 owes its even lower resistivity to both high structure and low particle density, while EC Black owes its lowest resisitivity to an extremely low particle density caused by the presence of a large number of hollow-shell particles, as indicated by electron micrography. It was shown that the resistivity of vulcanizates loaded with EC Black is practically unaffected by deformation up to 150%, in contrast to other conductive blacks at comparable resistivities. It has been observed that increasing the degree of loading leads to a lower limit of resistivity, about equal for all of the blacks. The various phenomena could be explained by the concept that the resistivity of carbon black loaded vulcanizates resides in the gaps between particles or aggregates and is determined by a process of electron tunneling.

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A correlation between the radiation-induced nine-ine electron spin resonance signal and the unstable component of the optical absorption in the near ultraviolet in poly-(methyl methacrylate) is made on the basis of the radiation dose relationship, the dependence of production on irradiation temperature at a constant radiation dose, and on the fading of both signals on oxygen ditrusion into the poly(methy1 methacrylate) after irradiation. It is concluded that this correlation is applicable only immediately after irradiation and the stability of the initial radical is discussed with respect to the fadiig resulta. A process of radical decay and conversion is suggested to account for Merences found in the fading characteristics of the two signals.It waa discovered by one of us9 that the optical absorption formed on irradiation in the neighborhood of 300 nm consisted of an oxygen-stable and an oxygen-unstable component. In this paper the relatiomhip between the unstable component of the radiation-induced optical absorption in commercial PMMA and the free radicals will be discussed. Materials and MetbodsCommerical PMMA of two types was used. One type, designated P2, contained <0.50/, aliphatic peroxide as initiator and <1% monomer, the 'Present address:

l,l,2,2-Tetrafluoro-l,2-bis(piperidinothiocarbonyl)ethane (11). A 3.5-g (0.014 mol) sample of 8 was added dropwise to a solution of 2.55 g (0.03 mol) of piperidine in 25 ml of ether at room temperature. The reaction mixture was evaporated to dryness under nitrogen, and the yellow residue was recrystallized from hexane-benzene to give 3.0 g of the diamide as yellow crystals: mp 129-132°; uv (ethanol) Xmax 365 (e 161) and 296 µ O 20,900); 19F nmr (CCI3D) -95.0 ppm (s); 1H nmr (CCI3D) 1.77 (m, 18 H), 4.04 (m, 4 H), and 4.28 ppm (m, 4 H).