Mechanisms of propagation, transfer, and short‐chain branching reactions in the free‐radical polymerization of ethylene

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Abstract
The propagation, transfer, and short‐chain branching reactions in the free‐radical polymerization of ethylene were studied at temperatures of 20–80°C. under pressures of 160–400 kg. cm.2 by means of two‐stage polymerization with the use of a specially designed reaction vessel. In the first stage, the polymerization was carried out in the presence of AIBN as the initiator, and in the second stage, the propagation occurred with living radicals in the absence of the initiator. In the second stage the polymer yield is shown to increase with reaction temperature and pressure, and the molecular weight of the polymer reached constant values which were dependent upon the temperature when the contribution of the polymer formed in the first stage was very small. It is shown that in the second stage the rate of propagation, transfer, and short‐chain branching are all proportional to the second power of ethylene fugacity, and that the activation energies of these reactions are 5.7, 23.4, and 10.9 kcal./mole, respectively. The polymer has no terminal vinyl group. The mechanism of these reactions is discussed on the basis of kinetic and energetic results.