High Resolution Magic Angle Spinning (HR-MAS) 1H NMR investigation of the active surfaces of MgCl2-supported Ziegler-Natta catalysts: The MgCl2 matrix

"Classical" MgCl2-supported Ziegler-Natta Catalysts (ZNC) continue to monopolize the industrial prodn. of isotactic polypropylene. There is a growing awareness of the inherent competitive edge of these low-cost systems over single-center ones (primarily metallocenes), and of the potential for further improvement, particularly if a deeper insight into the structure of the catalytic surfaces and the mechanisms of their modification by means of electron donors can be achieved. In the framework of a project ultimately aiming at the implementation of ZNC with known and controlled surface structure, we started a re-visitation of the whole area by using High Resoln. Magic Angle Spinning 1H NMR. In this paper, we report on the results obtained for the neat MgCl2 matrix and for model MgCl2/electron donor adducts, which yield information on the relative stability of the lateral surfaces of the MgCl2 crystallites, and on the dynamic features of donor chemisorption as a function of donor nature and extent of surface coordinative unsatn. In our opinion, this exptl. approach opens new possibilities in the investigation of these complicated and challenging catalyst systems.