Vol. 70 was added. With styrene the thermal polymerization proceeded at a convenient rate, while methyl acrylate and methacrylate apparently contained enough adventitious catalyst to effect reaction. Vinyl acetate samples were polymerized by irradiating with a mercury vapor lamp. Samples and heating times were chosen to yield mg. of polymer. Methyl methacrylate and acrylate polymers were worked up by precipitating three times from ethyl acetate with petroleum ether in a 50-ml. centrifuge tube. The polymers were then redissolved in approximately 5 cc. of ethyl acetate and transferred in portions to tared aluminum dishes 26 mm. in diameter and 3 mm. deep and the solvent evaporated under an infrared lamp. The centrifuge tubes were washed with additional benzene and the dishes dried under the lamp overnight (approx. 8 in. from a 250-watt bulb was found to yield a smooth bubble-free film). Blank experiments showed that this treatment was adequate to remove all solvent, and yields were determined by weighing the dishes. Relative polymer activities were then measured by placing the dishes covered by a mask with a hole approximately 20 mm. in diameter under the thin mica window of a Radiation Counter Laboratories Mark I Model 2 Geiger-Mueller counter attached to an Instrument Development Laboratories Scaling Circuit. For the styrene and vinyl acetate experiments, the polymer isolation procedure was modified in that the partially polymerized samples were transferred to a large side-arm test-tube and unreacted monomer distilled off in vacuo at room temperature.The polymer was redissolved (in chlorobenzene or toluene, respectively) and the solvent again distilled off. This procedure was repeated twice more and the residual polymer transferred to an aluminum dish for counting.Actually, for the determination of the relative activity, R, theoretical activities of completely polymerized samples were calculated from a completely polymerized polystyrene sample, correcting for differences in mercaptan concentration in the reaction mixtures and polymer densities. Thus the measured activity of the styrene sample was multiplied by 1.06/1.19 for comparison with methacrylate since, because polymethacrylate has a greater density, the measured (3-radiation is coming from a thinner layer of the polymer surface. Counts of relative activities were always extended to several thousand impulses to avoid significant random variations and comparisons of any set of polymers with the standard were always carried out consecutively since background count and sensitivity of the instruments varied from day to day. Summary 1. A convenient method for the synthesis of radioactive mercaptans from zinc sulfide containing S3S has been worked out.
Six highly refined hydrocarbon jet fuels were thermally cracked in a flow reactor at a wall temperature of 1200°F. (reaction temperature of 1070°to 1100°F .) and pressures from 200 to 1000 p.s.i.g. The calculated first-order rate constants for highly paraffinic and highly naphthenic fuels containing negligible unsaturates were affected only slightly by pressure and were about twice as large as the value for pure m-hexadecane under the same conditions. At 500 p.s.i.g., a paraffinic fuel containing 16 weight % olefins had a first-order rate constant approximately 2.5 times greater than those for fuels containing negligible olefins; however, this decreased rapidly with increased pressure. Product composition was determined as a function of the degree of reaction and the results were fitted to a kinetic model.
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