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SynopsisThe kinetic3 of the photopolymerization of styrene in bulk and in dilute systems in the presence of benzoin isobutyl ether as photoinitiator have been examined. The values of the intensity exponent, calculated at different temperatures or at different styrene concentrations, and the monomer exponent, calculated at various intensities, showed significant departure from those predicted by the ideal kinetic scheme, particularly at high intensity, at low temperature, or at low styrene concentrations. Low molecular weight polymer was the dominant product when high light intensity or low polymerization temperature was used. As the temperature was raised, however, or as the intensity was reduced, a high molecular weight polymer became progressively more important. Kinetic and molecular weight data suggest that at low temperature, high intensity, and/or at low monomer concentration, the benzoyl radical is the dominant initiating species; and the benzyl ether radical was consumed mainly in the termination step. At low intensity, high temperature and/or high monomer concentration, however, it appears that both benzoyl and benzyl ether radicals initiated polymerization.

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.

SynOPhStudies have been made of the y-radiation-induced polymerization of methyl methacrylate in bulk, in the solid state a t a temperature of -65°C. and a radiation intensity of 346,000 rad/hr. The reaction was found to have an extremely long induction period (-50 hr.) when pure monomer was used, and to be firsborder with respect to polymer concentration. This firsborder dependency was confirmed by a series of irradiations in which 0.6% poly(methy1 methacrylate) was dissolved in the monomer before irradiation. These irradiations showed no induction period. Nuclear magnetic resonance spectroscopy indicated a much more heterotactic polymer than that obtained in the liquid state a t -49°C.

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