Ziegler-Natta (ZN) catalysts for isotactic polypropylene (iPP): a glimpse inside the black box

Classical ZN catalysts still have the monopoly of industrial iPP production. With their complex formulation, including an ‘activated’ MgCl2 support, a Ti precursor, an Al-alkyl activator, and in most cases a properly chosen pair of electron donor modifiers, these systems are rightfully considered, in many respects, ‘black box’ ones, and so far no true cases of active surface design have been reported. On the other hand, it is indeed possible to tailor application based on trial-and-error, primarily by means of a smart selection of the electron donors, recently also under the guidance of ‘black-box’ QSAR models. In the latter respect, a collaboration between SABIC and this laboratory, making intensive use of High Throughput Experimentation (HTE) screening methods, gave important results, including the identification of electron donors with improved performance. In parallel with the ‘black-box’ QSAR, a fundamental study of the catalysts is also in progress; moving from the HTE database, added with statistical analyses of 13C NMR polymer microstructure, quenched-flow kinetic experiments, and periodic and cluster DFT calculations, quantitative hypotheses on the interactions between the various catalyst system components and the local structure of the active surfaces are being formulated, and it happens more and more that partial views of what hides in the ‘black-box’ are obtained. In this presentation, we will describe what we saw, along with the actions that, in our opinion, are necessary to fully remove the cover and highlight the box.