Effect of Modifiers on the Performance of Ziegler-Natta Catalysts in Olefin Polymerization

Catalyst activity is one of the most important criteria in polymerization processes. In
a catalyst system, the activity may depend on the polymerization conditions such as
temperature and pressure. However, at a fixed condition of polymerization, it would be
undesirable to change the temperature and pressure of the system in order to enhance the
activity of the catalysts. Accordingly, scientists are encouraged to increase the amount of
catalyst and/or prolong the polymerization time which are not economically approved. In
recent years, modifiers have been used to enhance the activity of Ziegler-Natta catalysts.
They do not have any impact on the polymerization mechanism but affect the final
properties of the final polymer including number-average molecular weight and weightaverage
molecular weight. They have also played a role in rising melting temperature,
crystallinity, bulk density and particles size to a smaller extent. Because of the special role
of the modifiers in Ziegler-Natta based olefin polymerization processes, different types of
promoters are introduced here. In this respect, the effect of different modifiers including
organo-halides as well as metal-halides and metalloids on the activity of Ziegler-Natta
catalysts and final properties of polymer is explained in detail.