Preparation And Performance Of Highly Branched Polyethylene Synthesized By Alpha-Diimine Nickle

Using homogeneous a-diimine nickel and supported a-diimine nickel catalysts as main catalysts respectively, and MAO as cocatalyst, the slurry polymerization of ethylene was carried out. Effects of the symmetry of ligands backbone, the support materials, and the supporting methods of catalysts on the catalytic activity, the kinetic evolution, the microstructure and performance of polyethylene in the polymerization under various reaction conditions were studied, and the difference between HBPE (highly branched polyethylene) and POE (Ethylene-co-octene), and the modification of the performance of iPP (isotactic polypropylene) were studied also.The effect of substituents of ligands backbone of a-diimine nickel on the branching distribution of polyethylene was investigated. The maximum activity increased from 1397 kg PE/mol Ni-hr to 1855,1924 kg PE/mol Ni-hr as the substituents of ligand backbone varied from R2=CH3 to R2=CH2CH3, R2=CH2CH2CH3 (all R1=CH3). The long branching in HBPE (40℃obtained) increased gradually from 4.9 to 24.3,17.1/1000C as the substituent of ligand backbone varied from R2=CH3 to R2=CH2CH3, R2=CH2CH2CH3 (all R1=CH3). Besides the asymmetry on the ligand banckbone could increase the molecular weight of polyethylene, it could improve the thermo-stability of catalysts also. The kinetic evolution revealed, the catalytic activity increased steeply at the start of polymerization, then gradually decreased, and it reached the stable stage at about 15 minutes. The catalysts with asymmetric substituents on the ligand backbone had higher activities mainly in the start of 15minutes.The effect of supports organo-silica and inorganic silica on the activities of immobilized catalysts, the microstructure and performance of polyethylenes were investigated. The organo-SiO2 had mainly three virtues for catalyst supporting. Firstly, the activities of organo-silica immobilized catalysts (SC2, SC3), which had asymmetric substituents on the ligand backbone, were higher than that of inorganic immobilized catalysts (SCI). But the activities of catalysts with symmetric substituents on the ligand backbone (SC5, SC6) were similar whether they were supported on organo-silica or inorganic silica. Furthermore, the activities of catalysts with symmetric substituents on the ligand backbone reached the peak at about 20℃under optimized Al/Ni (Al/Ni=600) ratio, but the activities of the immobilized catalysts with asymmetric substituents on the ligand backbone increased accompanying the increasing Al/Ni ratio, and the catalysts had higher activities under lower Al/Ni ratio when the organic fraction in support was higher. The maximum activity (20℃, Al/Ni=600) of catalysts increased from 475.0 kg/mol Ni-hr to 709.6,808.5kg/mol Ni-hr as the organic fraction varied from 0 to 20%,50%. The second virtue of organo-silica is to suppress reactor fouling due to restrain the dropping of immobilized catalysts during ethylene polymerization. The third virtue of organo-silica is to suppress the production of polyethylene at melting point about 120℃, because the organic group, which inclined to configurate on the surface of supports during support preparation, decreased the immobilization of catalysts on the hydroxyl of inorganic SiO2. The melting curves of polyethylenes synthesized by organo-silica immobilized catalysts (SC2, SC3) were similar to that synthesized by homogeneous catalysts. The branching degree of polyethylenes was moderate (SC2,69.1/1000C; SC3,48.4/1000C) at higher polymerization temperature (40℃) because of the hindrance of supports when the catalysts were immobilized on organo-silica. On the contrary, the branching degree of polyethylenes was higher because of the dropping of catalysts when the catalysts were immobilized on inorganic silica. The kinetic evolution disclosed the kinetic curve of catalysts was increase-drop type.The PE/iPP in-reactor alloys by ethylene gas-phase polymerization in iPP granular particles were prepared. Gas-phase polymerization could avoid reactor fouling and facilitate the separation process. The activities reached the peak at 20℃and the polyethylene fraction could be more than 20wt% in the obtained PE/iPP in-reactor alloy. There existed three polymers in the alloy, which were polyethylene synthesized by "free"α-diimine nickel catalyst, ethylene synthesized by MgCl2/SiO2-immobilizedα-diimine nickel catalyst and iPP. The melting point and crystallization point of polyethylene, synthesized by "free"α-diimine nickel catalyst, shift toward low temperature and that of polyethylene synthesized by MgCl2/SiO2-immobilizedtedα-diimine nickel catalyst shift a little. 13C-NMR analysis disclosed the branching degree of the obtained polyethylene was less than half of that synthesized by homogeneous catalyst and the obtained polyethylene was made up of polyethylenes with different branching degree because of mass transfer limit. The performance of catalyst and polyethylene were investigated. Polyethylene was obtained in heterogeneous slurry polymerization by bis-(2,6-dimethylphenyl) pentane nickel dibromide immobilized on iPP granular particles with a little polar units-CH(CH3)CH2CH2CH2C(CH3)2OH. The reactor fouling didn't exist below 50℃and the morphology of the obtained alloy particles duplicated the morphology of iPP particles in toluene by slurry process. The polyethylene fraction in the HBPE/iPP alloy could be more than 60wt% in half an hour polymerization and the activities of iPP-immobilized catalysts were about one-fifth (20℃,361.8kg/mol Ni-hr) and one-third (40℃,417.5kg/mol Ni-hr) of homogeneous catalyst. Polyethylenes (PEs) with branching degree from 20.0 to 130.4/1000C were prepared as the polymerization temperature varied from 20℃to 50℃and the branching distribution of PEs was similar to that of PEs synthesized by homogeneous catalyst. According to DSC analysis result, two kinds of polyethylene were obtained by catalysts immobilized on iPP chain and MgCl2/SiO2 separately. The fraction of polyethylene prepared by the MgCl2/SiO2 supported catalyst was so low that the melting peak could not be figured out, and the melting point shifted a little. The melting point of polyethylene prepared by the PP-chain supported catalyst shifted from 107℃to 29℃accompanying polymerization temperature varied from 20℃to 50℃.The performance difference between HBPE and POE, and their modification to the performance of iPP were investigated. The interaction existed between HBPE and POE, and HBPE could enhance the interpenetration between POE and iPP in HBPE/POE/iPP mechanical blending. DSC analysis disclosed a new phase occurred at about 120℃in HBPE/POE/iPP65 alloy."Ocean-island" structure (20℃), inter-penetration structure (30℃) could be observed with SEM in HBPE/iPP in-reactor alloy obtained according to chapter 6, but two-phase structure could not be observed in HBPE/iPP mechanical blending.