A kinetic study of the oxygen‐initiated polymerization of ethylene

The kinetics of the oxygen‐initiated polymerization of ethylene show some features previously unrecorded in vinyl polymerizations. Preceding formation of polyethylene, there is an induction period which depends strongly on temperature and pressure but only slightly on oxygen concentration. During the induction period the rate of oxygen consumption increases exponentially with time and approximately one‐half of the oxygen is consumed prior to polymerization which can take place only if certain critical conditions depending primarily on pressure and oxygen concentration are exceeded (critical boundary). A formal reaction mechanism with degenerate kinetic chain branching is postulated from which the most important experimentally observed relations can be deduced. The induction period for polymerization then becomes the reciprocal branching factor for the oxidation of ethylene and the critical boundary a kinetic limit familiar in hydrocarbon oxidations with degenerate branching. The shape of the critical boundary can be derived by postulating, in addition, a sequence of reaction steps similar to those frequently used to represent the low temperature oxidation of hydrocarbons. Under the conditions investigated, the initiation mechanism dominates the polymerization, and an interpretation of the propagation and termination steps cannot be made.