Iminopyridine Ni(II) Catalysts Affording Oily Hyperbranched Ethylene Oligomers and/or Crystalline Polyethylenes Depending on the Reaction Conditions: Possible Role of In Situ Catalyst Structure Modifications

Macromol Pub Date : 2021-03-24 DOI:10.3390/MACROMOL1020010
I. D’Auria, Z. Saki, C. Pellecchia
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引用次数: 4

Abstract

Nickel-based ethylene polymerization catalysts have unique features, being able to produce macromolecules with a variable content of branches, resulting in polymers ranging from semicrystalline plastics to elastomers to hyperbranched amorphous waxes and oils. In addition to Brookhart’s α-diimine catalysts, iminopyridine Ni(II) complexes are among the most investigated systems. We report that Ni(II) complexes bearing aryliminopyridine ligands with bulky substituents both at the imino moiety and in the 6-position of pyridine afford either hyperbranched low molecular weight polyethylene oils or prevailingly linear crystalline polyethylenes or both, depending on the ligand structure and the reaction conditions. The formation of multiple active species in situ is suggested by analysis of the post-polymerization catalyst residues, showing the partial reduction of the imino function. Some related arylaminopyridine Ni(II) complexes were also synthesized and tested, showing a peculiar behavior, i.e., the number of branches of the produced polyethylenes increases while ethylene pressure increases.
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亚氨基吡啶镍(II)催化剂根据反应条件产生油性超支化乙烯低聚物和/或结晶聚乙烯:原位催化剂结构修饰的可能作用
镍基乙烯聚合催化剂具有独特的特性,能够产生具有可变分支含量的大分子,从而产生从半结晶塑料到弹性体到超支化无定形蜡和油的聚合物。除了Brookhart的α-二亚胺催化剂外,氨基吡啶Ni(II)配合物是研究最多的体系之一。我们报道,根据配体结构和反应条件的不同,携带aryliminopyridine配体的Ni(II)配合物在吡啶的亚基和6位都有大体积取代基,可以产生超支化的低分子量聚乙烯油或普遍的线性结晶聚乙烯,或两者兼有。通过对聚合后催化剂残基的分析,发现在原位形成了多个活性物质,显示了亚胺功能的部分还原。本文还合成并测试了一些相关的芳氨基吡啶Ni(II)配合物,结果表明,随着乙烯压力的增加,所合成的聚乙烯分支数增加。
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