SPECTROSCOPIC CHARACTERIZATION OF IMINOPYRIDINE IRON COMPLEXES FOR THE POLYMERIZATION OF MYRCENE: INVESTIGATION OF THE ACTIVE SITES

Elastomers are amorphous and flexible polymers that can largely deform themselves when a stress is applied and can partially or completely recover when the stress is removed. These properties, which are not observed in stiff materials, such as metals and ceramics, make elastomers irreplaceable in many applications, such as in films, dampers, adhesive, rubber bands and vehicle tires. Nowadays, most of the elastomers are produced from monomers obtained from fossil sources (such as isoprene), by using expensive and rare transition metal and lanthanide catalysts which sometimes are hostages of problematic geopolitical contexts, making them unsustainable in the long term. A key to make elastomers more sustainable is to develop a process to synthesize elastomers from renewable resources, like myrcene, exploiting catalysts based on abundant, non-toxic and cheap metals, such as iron. The objects of this thesis work are iminopyridine iron complexes designed for the polymerization of bio-terpenes (mainly myrcene) to give elastomers with high molecular weight. The complexes were synthetized in the laboratories of SCITEC-CNR in Milan and tested in isoprene and myrcene polymerization in the context of a previous Master thesis work. Herein, instead, we focused on the spectroscopic characterization of the iron complexes by means of time-resolved UV-visible spectroscopy. The most interesting and challenging aspect of the project was the study of the interaction between the iminopyridine iron complexes and the activator (MAO), to understand the nature of the active site (or active sites?). The obtained spectroscopic results suggest that the active species change upon increasing the aging time (i.e., the time of pre-contact of the molecular precursors with MAO). Hence, focused polymerization tests were performed at SCITEC-CNR to investigate the effect of the aging on both the catalytic activity and the polymer properties. The polymers obtained were characterised with FTIR and analysed with gel permeation chromatography (GPC). Even though the true nature of the active site is far from being understood and would require the developing of new experiments supported by computational studies, the results obtained are encouraging. Iminopyridine iron complexes look as promising catalysts for the development of new sustainable elastomers based on bio-sources.