Modeling and measurement of high pressure ethylene polymerization long-chain branching and molecular weight distributions

Polyethylene samples produced by the free-radical high-pressure process exhibit bimodal molecular weight distributions (MWDs), despite being made in a well-mixed continuous tank reactor. MWD simulations provide valuable insights to the relative importance of β-scission and long-chain branching in the system. The rate coefficient for branching relative to propagation is 0.01-0.03, and 2-4 % of the secondary radicals formed by intermolecular H-abstraction undergo scission. This fraction, although small, not only has a profound effect on the shape of the MWD, but is also sufficient to prevent gel formation.