Synthesis of bimodal molecular weight distribution polyethylene with α-diimine nickel(II) complexes containing unsym-substituted aryl groups in the presence of methylaluminoxane
- 作者：Hao Zou ; Sheng Hu ; Huahua Huang ; Fangming Zhu ; Qing Wu
- 关键词：Unsymmetrical α ; -diimine nickel(II) complexes ; Polyethylene ; Methylaluminoxane ; Bimodal molecular weight distribution ; Stereo-isomers
- 刊名：European Polymer Journal
- 出版年：2007
- 期刊代码：35_00143057
- 类别：ms
- 出版时间：September 2007
- 卷：43
- 期：9
- 页码：3882-3891
- 文件大小：432 K
摘要
A series of unsymmetrical complexes of 2,3-bis(2-phenylphenyl)-butanediimine nickel(II) dibromide (complex 1), 1,4-bis(2-isopropyl-6-methylphenyl)-acenaphthenediimine nickel(II) dibromide (complex 2) and meso- and rac-1,4-bis (2,4-di-tert-butyl-6-methylphenyl)-acenaphthenediimine nickel(II) dibromide (meso-3 and rac-3) were synthesized and activated by methylaluminoxane (MAO) for ethylene polymerization. By 13C NMR characterization, meso- and rac-stereo-isomers were detected in the condensation products resulting from the reaction of unsym-substituted anilines with diketones. It was notable that meso- and rac-isomers in ligand 1 or ligand 2 could not be separated owing to their interconversion, however, meso- and rac-isomers in ligand 3 could be isolated and identified by X-ray diffraction and NMR analysis. At low polymerization temperatures, complex 1/MAO afforded polyethylene with bimodal molecular weight distribution, while complex 2/MAO prepared polyethylene with single-modal distribution. Moreover, by raising polymerization temperature or extending time of catalyst aging, bimodal molecular weight distribution polyethylene was also produced by complex 2/MAO. The hypothesis of bimodal molecular weight distribution polyethylene synthesized by unsymmetrical α-diimine nickel(II) complexes was supported that the molecular weight of polyethylene produced by rac-3/MAO was significantly higher than that produced by meso-3/MAO under identical polymerization conditions. A unique methodology to prepare polyethylene with bimodal molecular weight distribution was demonstrated.