Methylaluminoxane-activated polyolefin precatalysts: An applied research approach

The scope to judiciously design versatile methylaluminoxane (MAO) anions, for a selected industrially prospective non-Ziegler-Natta precatalyst, is very wide. Nevertheless, the non-Z-N industrial processes are at the infancy stage. Therefore, this study addresses MAO-activated polyolefin precatalysts from an applied research perspective. In particular, it reports a novel conceptual framework that can be easily experimented to evaluate the effects of hydrodynamic boundary layer mass transfer (HBL), MAO anion design, and comonomer steric hindrance on MAO-activated ethylene polymerization. This approach was illustrated by conducting homo- and isomeric copolymerization of ethylene with 1-hexene and 4-methyl-l-pentene in the presence of bis(n-butylcyclopentadienyl) zirconium dichloride (ⁿBuCp)₂ZrCl₂, using (i) MAO anion 1 (unsupported [MAOCl₂) and pseudo-homogeneous reference polymerization, and (ii) MAO anion 2 (supported Si-O-[MAOCl₂]^-) and in-situ heterogeneous polymerization. The peak, melting and crystallization temperatures and % crystallinity were mathematically correlated to the parameters of microstructural composition distributions, melt fractionation temperatures, and average lamellar thickness. These new relations showed to be insightful. The comonomer-induced enchainment defects and the eventual partial disruption of the crystal lattice were successfully modeled using Flory and Gibbs-Thompson equations.