NOTES 543induced vinyl polymerization. As is the case in radiation of monomers to produce polymers, no catalysts are required. However, by this technique, a small quantity of polymer can be irradiated with gamma rays, stored at room temperature or in a refrigerator, and later used to initiate the polymerization of a larger quantity of monomer. The irradiated polymer is obviously replacing the usual peroxide catalysts. This technique should also have utility where some ingredient of the polymerized end product is sensitive to gamma radiation or peroxide catalysts.Polymethyl methacrylate (Eastman Kodak), purified by precipitation from a benzene solution with methanol and freeze-dried, was deoxygenated by pumping at mm. for several hours. Irradiation was carried out using a 5000 curie Cow source a t a dose rate of 9 X 106 rep/hr., at liquid nitrogen temperatures. After irradiation, deoxygenated methyl methacrylate was mixed with the polymer, very rapid solution taking place. The quantities used in these experiments were 100 mg. of polymer and about 1 ml. of monomer.When polymethyl methacrylate was irradiated for 5 hours no appreciable amount of free radical was formed, as evidenced by the fact that no polymerization was induced upon addition of methyl methacrylate. After 24 hours of irradiation polymethyl methacrylate produced a transparent gel in two weeks' time after mixing the polymer with methyl methacrylate. The viscosity was seen to increase within 12 hours of mixing, and continued to increase until the gel stage was reached. That "trapped" free radicals were produced in the irradiated polymethyl methacrylate was demonstrated by its ability, after standing a t room temperature for two days following irradiation, to induce the polymerization of methyl methacrylate to a gel. Even after standing a t room temperature for one week, the irradiated polymer induced some polymerization of methyl methacrylate, but not to the gel stage. The effect of longer irradiation times is presently being studied. Polymerization of Ethylene in the Liquid PhaseWhile relatively little kinetic data have been published about the homopolymerization of ethylene a t high temperatures and pressures, even less has been published about the homopolymerization of ethylene in the liquid phase. A number of patents do exist in this These patents do not contain sufficient data to allow the calculation of kinetic data.We wish to report some results obtained by polymerizing ethylene via free radical catalysts at 0 f 0.5"C. under its autogenous pressure (about 40 atm.). The polymerization was initiated by uv light using dimethyl azobisisobutyrate as the source of free radicals, since this compound was found to be soluble in ethylene a t 0°C. The intensity of light entering the cell was measured using uranyl oxalate and potassium ferrioxalate as photolytes. Also, the decomposition rate of the initiator was measured in pure hexane.
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