Initiation and propagation in γ‐radiation‐induced polymerization of ethylene

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Abstract
The initiation and propagation reaction in γ‐ray‐induced polymerization of ethylene was studied by the two‐stage irradiation method, i.e., a first stage in which initiation and propagation occur at a high dose rate, and a second stage where only the growth of polymer radical occurs. The rate of initiation is calculated from the amount of polymerized monomer and the degree of polymerization as the rate of increase in the number of polymer chains. The initiation rate is shown to be proportional to the ethylene density in the reactor and dose rate. GR of radical formation is found to be about 1.6 at 30°C. at a dose rate of 2.5 × 104 rad/hr. and is almost independent of ethylene density but decreases slightly with increasing irradiation dose rate. The lifetime of the growing polymer chain radical is shown to be long at normal temperature. The absolute propagation rate is proportional to the square of ethylene fugacity and depends on dose rate to some extent. For chain growth, irradiation of low dose rate is necessary. The apparent activation energy for the propagation reaction is −9 kcal./mole.

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