A 2ND LOOK AT MODELING THE MULTIPLICITY OF ACTIVE-SITE TYPES OF ZIEGLER-NATTA CATALYSTS WITH FLORY AND STOCKMAYER DISTRIBUTIONS

The presence of multiple site types on the surface of heterogeneous Zi egler-Natta catalysts is generally used to explain the production of p olyolefins with broad and sometimes multimodal distributions of molecu lar weight (MWD) and chemical composition (CCD). These distributions c an be modelled as a superposition of several Flory's and Stockmayer's distributions for each site type. However, several individual distribu tions are generally needed to properly describe MWD and CCD, making it difficult to assign these distributions to chemically distinct cataly st sites. In the model proposed herein, Flory's and Stockmayer's distr ibutions are used to explain the underlying polymerization mechanism o n each site type, but catalyst site-surface interactions are considere d to broaden these distributions. As a result, fewer Flory's and Stock mayer's distributions are required to describe broad and multimodal MW Ds and CCDs.