Kinetics of the γ‐radiation‐induced polymerization of ethylene

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Abstract
Studies of the rates of γ‐radiation‐initiated polymerization of ethylene in the gas phase at 22°C., 40–70 atm. and 380,000 r/hr. have shown that the rate expressions show a good correlation with the relations expected from kinetic considerations if the density is used to express the ethylene concentrations. In this range of temperature and pressure, the density, pressure, and fugacity relations for ethylene differ significantly from those at the elevated pressures which have been used in previous rate studies. Use of fugacities in the rate expression log (rate) = a + b log x, where x = p, f, or d, gives a value of 10.4 for the b term; use of pressure gives a value of 5.0; and use of density gives a value of 2.4. This last value is closest to that predicted (2.0) from a kinetic analysis which takes into consideration an initiation step dependent on monomer concentration and termination by primary radicals. Studies of the liquid‐phase polymerization over the temperature range of 5 to −40°C. give an activation energy of 4.4 ± 1.8/kcal./mole. Infrared analysis of the product indicates that short‐chain branching is much less (0–1.2 vs. 2–3 branches per 100 carbon atoms) than for polyethylenes prepared at higher temperatures. Relations between solution and melt viscosities indicate a high degree of long‐chain branching in the polymer.

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