Reactivity and immobilization of group IV single-center olefin polymerization catalysts

PhD ceremony: Ms. E. Novarino, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Reactivity and immobilization of group IV single-center olefin polymerization catalysts

Promotor(s): prof. B.L. Feringa, prof. B. Hessen

Faculty: Mathematics and Natural Sciences

A large fraction of the commercially manufactured crystalline polyolefins are produced in large-scale slurry and gas-phase processes, which require the polymerization catalyst to be anchored on a solid support to obtain a satisfactory product morphology. Therefore, there is considerable interest in the development of suitable and well-defined supports for single-center olefin polymerization catalysts. By Elena Novarino a readily reproducible and quantifiable procedure has been developed to prepare well-defined silica supports with tethered fluorinated borate anions that should provide a good platform for the detailed study of the behavior of immobilized cationic transition-metal catalysts in a quantitative manner.

The major objective of immobilization of metallocene catalysts is to merge their single-center characteristics (high activity, narrow molecular weight distribution, stereoselectivity) with the advantages of supported catalyst technologies (good morphology, high bulk density) for their implementation in gas-phase and slurry polymerization processes. Although several catalyst systems have been developed, little information is available on the effect of the immobilization process on the nature and stability of active sites.

Novarino has improved the shelf-life of cationic transition-metal polymerization catalysts by intramolecular coordination of an olefinic substrate of the type CH2=CH-(CH2)nSR bearing a Lewis base functionality with formation of sufficiently stable chelate species. This allows to study and quantify the transformations of the activated species at defined time intervals via NMR spectroscopy techniques.

As the strength of the intramolecular interaction can be weakened by increasing the length of the spacer between the Lewis base and olefinic moiety, a good compromise between thermal stability and reactivity under reactor conditions can be achieved, resulting in a less stable chelate which is readily opened by ethylene.