Design And Synthesis Of Titanium And Zirconium-Based COF Materials And Their Performance In Ethylene Polymerization

The development of human society and the progress of science and technology have led to the demand for polyolefin materials becoming strong in national economic sectors as healthcare,pharmaceuticals,automotive and instrument manufacturing industries,construction,electronics,agriculture,communication devices,consumer products,food and non-food product packaging,etc.The performances and polymerization results of conventional industrial olefin polymerization catalysts cannot meet the demand for better life.In order to develop novel catalysts for the fine production of polyolefins and to find new generation of economical and environmentally friendly heterogeneous polymerization systems,much effort has been made to control the selectivity of olefin insertion and improve the activity of catalytic systems based on nanoconfined porous materials.Covalent organic framework materials（COFs）are organic porous crystalline materials composed of small organic molecular building blocks of light elements（C,H,O,N,and B,etc.）.Topologically predesignable COFs are a class of porous polymer supports with high potential and wide functionalization applications,which are suitable for olefin polymerization.1.Design and synthesis of Zr-based COF materials and their performance study of ethylene polymerizationThe four monomers,2,5-dihydroxyterephthal aldehyde（Da）,1,3,5-tris（4aminophenyl）benzene（Tb）,2,4,6-tris（4-aminophenyl）-1,3,5-triazine（Tt）and 4,4’,4"-（1,3,5triazine-2,4,6-triyl）tris（2,6-dimethylaniline）（Td）were obtained by aldolamine condensation reactions to give a series of COFs with different pore sizes and volumes:TbDa,TtDa and TdDa.Among them,the pore size of TdDa is the largest,and the mutual repulsion between the interlayer moieties leads to the largest pore volume of TdDa due to the largest number of functional groups in the one-dimensional channels.The pore size and pore volume of TbDa and TtDa do not differ much.The ZrCl4 coordinates with the O of phenolic hydroxyl groups and N of imine in the COFs channel（metalized COF）to form salicylaldehyde imine Zr catalysts（supported FI-Zr）.The structures of the three Zr-COFs were characterized by FTIR,PXRD,BET,SEM and XPS.Meanwhile,the performance of the three Zr-COFs for ethylene polymerization was further investigated.Among them,Zr-TdDa has the largest ethylene polymerization activity(4.3×10⁴ gPE·mol_Zr^-1·h^-1)and its products have wide molecular weight distribution（D=2.0-2.8）,while the polymerization activities of Zr-TbDa and Zr-TtDa are 2.8×10⁴ and 3.0×10⁴ gPE·mol_Zr^-1·h^-1,respectively.However,the molecular weight distribution for the production of polyethylene ranged from 1.9 to 2.7.2.Design and synthesis of Ti-based COF materials and their performance study of ethylene polymerizationBy aldol-amine condensation reactions,we have developed four monomers,Da,Tb,Tt and Td were integrated to obtain a series of COFs with different pore sizes and pore functionalizations:TbDa,TtDa and TdDa.TiCl₄ was coordinated with O of phenolic hydroxyl group and N of imine in the COF channels to form salicylaldehyde imine Ti catalysts（loaded FI-Ti）.The structures of the three Ti-COFs were characterized by FTIR,PXRD,BET,SEM and XPS.Meanwhile,the performance of the three Ti-COFs for ethylene polymerization was further investigated.Among them,Ti-TdDa has the maximum ethylene polymerization activity of 3.4×10³ gPE·mol_Ti^-1·h^-1(less than 4.3×10⁴ gPE·mol_Zr^-1·h^-1 of Zr-TdDa),which is ascribed to its lower ethylene insertion rate.However,Ti-TdDa can produce high molecular weight polyethylene（Mw up to 1.6 × 10⁶ g/mol,greater than 1.5 × 10⁶ g/mol of Zr-TdDa）,which is attributed to its lower chain transfer rate,facilitating the production of ultra-high molecular weight polymers.