Covalent Organic Framework-Supported Metallocene for Ethylene Polymerization.

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 -- Cp2ZrCl2 for ethylene polymerization. The COF-supported catalyst demonstrates a higher catalytic activity of 31.1 × 106 g/(mol·h) at 140 °C, compared with 11.2 × 106 g/(mol·h) of the homogenous one. The resulting polyethylene (PE) products possess higher weight-average molecular weight (Mw) and narrower molecular weight distribution (Ɖ) after COF supporting, i.e., Mw increases from 160 kDa to 308 kDa and Ɖ reduces 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 MPa 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 high-efficient olefin polymerization and high-performance polyolefins.