INSERTION (CO)POLYMERIZATION OF OLEFINS CATALYZED BY FIRST ROW TRANSITION METAL COMPLEXES

Since polyolefins are an integral part of everyday life and given the ever-growing global demand for these polymers, the insertion polymerization of olefins is one of the most industrially relevant synthetic reaction, widely investigated also in academia. It is in this context that this PhD project is located. The developed research activity was aimed at synthesizing new catalytic systems capable of stereochemically drive the polymerization of various (di)olefins, in particular cyclic olefins such as norbornene and its derivatives. The investigated catalysts are made up of two components: the organometallic complex (pre-catalyst) and an aluminum alkyl compound (co-catalyst or activator). Among the series of the organometallic complexes, during my PhD, complexes of the first row transition metals, i.e., titanium, vanadium, and chromium, bearing nitrogen and phosphorous based ligands were investigated. They were later applied as catalysts for the homopolymerization of ethylene, cyclic olefins (norbornene, dicyclopentadiene and norbornene derivatives) and 1,3-butadiene, and the copolymerization of ethylene with various cyclic olefins. Depending on the employed catalyst and the polymerization conditions, we obtained oligomers or high-polymers. All the products were carefully characterized with different techniques, in order to get more information on the properties of the obtained (co)polymers as well as on the polymerization mechanism. Norbornene and dicyclopentadiene oligomers were mainly obtained from titanium and chromium catalysts, activated by Et2AlCl and methylalumoxane (MAO), respectively, while cyclic olefin copolymers were obtained from the copolymerization of ethylene with cyclic olefins promoted by vanadium based catalysts. In addition, we demonstrated that some vanadium and chromium complexes, in combination with MAO, were active in the polymerization of 1,3-butadiene, affording poly(1,3-butadiene) with different microstructure (cis-1,4, trans-1,4 or 1,2) and stereospecificity (i.e., iso- or syndiotactic polymers), depending on the type of ligand. This study allowed to understand the correlations between the catalyst’s features and the polymerization outcome in terms of activity, regio- and stereoselectivity. Moreover, particular emphasis has been devoted to the study of the catalyst stability over the polymerization time and temperature. At the same time, particular interest has been developed toward the postpolymerization functionalization, as a strategy to modify some polymer properties (e.g., solubility and processability) and thus to obtain polymers hardly obtainable by direct (co)polymerization with polar (co)monomers. This PhD dissertation reports the results achieved during the three-year research activity, together with the main difficulties encountered and the actions put in place trying to overcome them.