Research On Design, Synthesis Of PX-Type Chromium Complexes And Their Applications In Ethylene Oligomerization/Polymerization

Ethylene is one of the largest chemical products around the world. Nowadays it was mainly used in the production of low molecular weight linear alpha olefin (straight chain terminal olefins with four carbon atoms or above) and high molecular weight polyethylene and its derivatives. In recent years, scientists at home and abroad have done a lot of research work around the development of catalysts on ethylene oligomerization and polymerization, and the development of transition metal catalysts with single active site for olefin polymerization was the research hotspot.In this dissertation,2-(diphenylphosphino) ethyl methyl sulfide ether ligand (PS),2-(diphenylphosphino) ethyl methyl ether ligand (PO) and (2-diphenylphosphanyl-ethyl)-dimethyl-amine (PN) ligand have been synthesized and characterized by’H NMR,13C NMR and 31P NMR, basing on the ternary catalytic system of PNP/CrCl3(THF)3/ methylalumoxane (MAO). These three ligands were reacted with CrCl3(THF)3 respectively to form chromium metal complexs, and the catalytic performance of chromium metal complexs for ethylene oligomerization/polymerization was studied:1) The effects of reaction temperature, reaction pressure, Al/Cr molar ratio, cocatalyst and solvent on the performance of PS-type chromium complexes for ethylene oligomerization/polymerization were investigated.2) The effects of reaction temperature, reaction pressure and solvent on the performance of PO-type chromium complexes for ethylene oligomerization/polymerization were investigated.3) The effects of reaction temperature, reaction pressure and solvent on the performance of PN-type chromium complexes for ethylene oligomerization/polymerization were investigated.The results revealed that the catalytic activity of PS-type chromium complex increased with the temperature first and then decreased, reaching maximum (65.00×103 g/molCr·h) at 60 ℃; the polydispersity index becomes larger as the temperature rises; the catalytic activity increased with the reaction pressure increased, and also the polydispersity index became larger as the pressure rose; under the condition that methylaluminoxane (MAO) was used as the cocatalyst and Al/Cr molar ratio was in range of 100-500, with the increase of Al/Cr molar ratio, the catalytic activity of PS-type chromium complex improved, the polydispersity index decreased, while there was no significant changes with the melting temperature; under the condition that dried methylaluminoxane (DMAO) mixed with triethylaluminum or triisobutyl aluminium as the cocatalyst and the Al/Cr molar ratio was 300, the catalytic activity reached maximum (379.00x103 g/molCr·h) when the the molar ratio of DMAO/triethylaluminum was 100/200; the catalytic activity of the catalytsts for ethylene oligomerization/polymerization and the selectivity of a-olefins when the solvent was toluene were higher than that when the solvent was cyclohexane. For the PO-type chromium complex, the catalytic activity increased with the temperature first and then decreased, reaching maximum (334.00×103 g/molCr·h) at 80 ℃; the polydispersity index increased with the temperature first and then decreased; but the melting temperature decreased with the temperature increasing; the catalytic activity improved with the pressure enhancing; the activity and selectivity to α-olefins when the solvent was toluene was much higher then that when the solvent was cyclohexane. For the PN-type chromium complex, the catalytic activity increased with the temperature first and then decreased, reaching maximum (436.00×103 g/molCr·h) at 80 ℃; the catalytic activity increased with the pressure; the activity and selectivity to α-olefins when the solvent was toluene was much higher then that when the solvent was cyclohexane.