Silica-supported metallocene catalyst poisoning: The effect of surface modification on the efficiency of the catalytic system

Covalent Organic Framework-Supported Metallocene for Ethylene Polymerization

The loading of homogeneous catalysts with support can dramatically improve their performance in olefin polymerization. However, the challenge lies in the development of supported catalysts with well-defined pore structures and good compatibility to achieve high catalytic activity and product performance. Herein, we report the use of an emergent class of porous material-covalent organic framework material (COF) as a carrier to support metallocene catalyst-Cp2 ZrCl2 for ethylene polymerization. The COF-supported catalyst demonstrates a higher catalytic activity of 31.1×106  g mol-1  h-1 at 140 °C, compared with 11.2×106  g mol-1  h-1 for the homogenous one. The resulting polyethylene (PE) products possess higher weight-average molecular weight (Mw ) and narrower molecular weight distribution (Ð) after COF supporting, that is, Mw increases from 160 to 308 kDa and Ð drops from 3.3 to 2.2. The melting point (Tm ) is also increased by up to 5.2 °C. Moreover, the PE product possesses a characteristic filamentous microstructure and demonstrates an increased tensile strength from 19.0 to 30.7 MPa and elongation at break from 350 to 1400 % after catalyst loading. We believe that the use of COF carriers will facilitate the future development of supported catalysts for highly efficient olefin polymerization and high-performance polyolefins.

Synthesis and ethylene polymerization reaction of dendritic titanium catalysts

The 1.0 G dendrimer (C₂₂H₄₈N₁₀O₄),3,5-di-tert-butylsalicylaldehyde and TiCl₄ · 2THF were used as the synthetic materials, and the dendritic salicylaldehyde imide ligand with substituent hindrance and its titanium catalyst were synthesized by the condensation reaction of schiff base. The structure of the synthesized products was characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, ultraviolet spectroscopy, electrospray mass spectrometry, and inductively coupled plasma mass spectrometry, The actual structure is consistent with the theoretical design structure. Activated methylaluminoxane (MAO) was used as a catalyst precursor for ethylene polymerization in the process of ethylene catalytic. The effects of ethylene polymerization were studied in terms of the Al/Ti molar ratio, reaction time, reaction temperature, polymerization pressure, and ligand structure of the catalyst. The results show at the reaction temperature of 25°C, the reaction time was 30 min, and the ethylene pressure was 1.0 MPa and Al/Ti was 1,000, the catalytic activity can reach 78.56 kg PE/(mol Ti.h). Furthermore, high-temperature GPC-IR, DSC, and torque rheometer were used to characterized the microstructure, thermal properties, and viscoelastic state of polyethylene samples obtained. The results showed that the product was ultra-high-molecular-weight polyethylene.