Osservazioni spettroscopiche su catalizzatori Ziegler-Natta con un Dietere come elettron-donatore

Ziegler-Natta catalysts are among the most important heterogeneous catalysts employed in chemical industry. In particular, the understanding of the role of electron donors in affecting the catalysts performance and the comprehension on how different synthesis routes affect the catalytic properties are topics that still have to be clarified and offer challenges for the future development of new and more performant catalysts. In this thesis, three Ziegler-Natta catalysts obtained by different synthesis procedures were studied, two catalysts were synthesised by chemical route and one trough mechanical route. The catalysts were synthesised by our colleagues at JAIST, Japan Advance Institute of Science and Technologies, in the frame of a joint project financed by the Dutch Polymer Institute (DPI). All the catalysts belong to the 5th generation of Ziegler-Natta catalysts having a 1,3- diether as internal donor, more precisely the donor used in these catalysts is 2-i-propyl-2-i-pentyl-1,3-dimethoxypropane. The thesis was devoted to characterize the pre-catalysts, the activated catalysts and catalysts during polymerisation of propene in order to obtain a complete picture of the properties of each catalyst at each stage of its “life”. The pre-catalysts were studied using Diffuse Reflectance UV-Vis spectroscopy and FT-IR spectroscopy, as described in paragraphs 3.1.1 and 3.1.2, respectively. The study of the precatalysts with Diffuse Reflectance UV-Vis spectroscopy was aimed to understand the local geometry of the supported Ti sites and their oxidation state. IR spectroscopy was used instead to get insights on how the donor interact with the surface of MgCl2 and of the precatalysts. The activated catalysts were also studied using Diffuse Reflectance UV-Vis spectroscopy and FT-IR spectroscopy, as described in paragraph 3.2.1 and 3.2.2 respectively. The study with DRS was devoted to show the differences in electronic properties between each activated catalysts and in respect the precatalysts. The activation procedure was carried out using triethyl aluminium (TEAl) TEAl with Al:Ti=2:1 and Al:Ti=1:1 as explained in paragraph 2.2.2. The study of activated catalyst with FT-IR spectroscopy was aimed to evaluate the accessibility of the surface active site grafted on MgCl2 monitoring in time the adsorption and desorption process of CO, used as probe molecule. The catalysts for this experiment were activated with Al:Ti=2:1. The catalytic performances and properties during polymerization were evaluated studying the polymerization kinetics of propylene and monitoring the polymerization of deuterated ethylene by IR spectroscopy, as discussed in paragraph 3.3.1 and 3.3.2, respectively. The study of the polymerization kinetics of propylene was carried out monitoring the variation of the propylene pressure during the polymerization reaction in order to assign an order to the reaction and obtain a rate constant for each catalyst. The polymerization of deuterated ethylene was instead followed using FT-IR spectroscopy, after the outgassing of CO in the previous experiment, to evaluate if the active sites remain active after the interaction with CO and just qualitatively the polymerization trends in respect this monomer for each catalyst and compare the results with the ones obtained from the polymerization kinetics of propylene. At last, chapter 4 will present some conclusions and perspectives.