MgCl2-supported catalysts for the propylene polymerization: effects of triethers as internal donors on the activity and stereoselectivity

Abstract

SUMMARY: The effects of triethers as internal donors on the activity and stereoselectivity of MgCl 2 -supported Ziegler-Natta type catalysts in the propylene polymerization were studied. In particular, we prepared and fully characterized some procatalysts of the type d -MgCl 2 /ID/TiCl 4 , where ID are internal donors such as di(ethyleneglycol) diethyl ether (DEGDEE) and di(ethyleneglycol) dimethyl ether (DEGDME). By aging these procatalysts with AlEt 3 (cocatalyst) we obtained d -MgCl 2 /ID/TiCl 4 /AlEt 3 catalytic systems, which were tested in the propylene polymerization in order to evaluate their catalytic performance. All polymerizations were carried out in the absence of both external donors (ED) and hydrogen. The productivity and the properties (Mn , and isotacticity index (I.I.)) of the polymers obtained were determined and the results compared with those obtained by using catalysts either lacking an internal donor or with ethyl benzoate as internal donor. The comparison pointed out that the presence of triethers lowers the productivity of the catalysts and increases their stereoselectivity. Polydispersity is also remarkably enhanced suggesting that a multiplicity of active catalytic sites characterized by different environments is present.

Mechanism of Propylene Polymerization with MgCl2-Supported Ziegler–Natta Catalysts Based on Counting of Active Centers: The Role of External Electron Donor

“…The industrial production of more than 50 million tons of isotactic polypropylene (PP) each year is based on catalyzed propylene polymerization with MgCl 2 -supported Ziegler–Natta catalysts. , Organic electron donors like esters, ethers, and alkoxysilanes are widely used in the catalyst preparation and polymerization processes, which play key roles in enhancing isotacticity and regulating molecular weight distribution of the PP products. − The electron donor added in the process of catalyst preparation is called the internal electron donor (Di), and the electron donor added in the polymerization process is called the external electron donor (De). In recent decades, the most commonly used catalyst in PP production contains phthalate as Di and alkoxysilane as De.…”

“…Since the discovery of TiCl 4 /Di/MgCl 2 –AlR 3 /De type propylene polymerization catalysts in the early 1980s, great efforts have been paid to disclosing and understanding the mechanism of electron donor effects, with an aim of further improving the chain structure of PP by applying new Di/De combinations. − The main role of Di has been proposed to control the amount and spacial distribution of TiCl 4 adsorbed on the MgCl 2 crystallite surface. − When TiCl 4 /Di/MgCl 2 type catalysts were treated with an AlR 3 /De mixture, most of Di molecules in the catalyst were found to be quickly replaced by De, implying that the De plays more important roles in the polymerization system. , The effects of De on stereoselectivity of active centers have been ascribed to reversible adsorption of donor on metal atoms (Mg or Ti) neighboring the central Ti metal of the active center. Busico et al proposed a three-site model to explain the effects of De on catalyst efficiency and polymer stereoregularity .…”

Polyethylenimines: Multidentate Electron Donors for Ziegler–Natta Catalysts

“…Thus, adjustment of a polymeric donor structure can offer a way to tailor the electron-donating properties. The polymeric electron donors have not yet drawn much attention, and only a few studies concerning the use of polyethers (e.g., polyethylene glycols and polytetrahydrofurans) have been published in the context of Ziegler–Natta catalysis. − Preparation and properties of MgCl 2 complexes with polyethylene glycols have been more widely reported in the field of electrolytes. − …”

MgCl2‐supported TiCl4catalysts containing diethyl norbornene‐2,3‐dicarboxylate internal electron donor for 1‐butene polymerization: Effects of internal electron donor configuration

“…The evolution of the ZN catalyst is mainly attributed to new and good ED that tune the active sites to improve the performance of the catalysts . Since the fourth generation of catalysts incorporating phthalate in MgCl 2 as an integral part of the support, referred to as the internal EDs (IEDs), many kinds of organic compound have been tested as IEDs over the past decades, including 1,3‐diether and succinates type IEDs. 1,3‐Diether provided an extremely high activity and isotacticity in propylene polymerization even in the absence of the external EDs (EEDs) that are added during the polymerization process, while succinates showed the high catalytic activity and the wide PDI of resulting polypropylene compared to the fourth‐generation catalysts .…”