Vinyl addition polymerization of norbornene catalyzed by β-iminoamine Ni(II) complexes/methylaluminoxane systems

Two nickel(II) complexes (A and B) bearing β-iminoamine ligands, [2-(ArNCH)-C6H4-NMe2] (La, Ar = 2,6-i-Pr2C6H3; Lb, Ar = 2,6-Me2C6H3), were synthesized and characterized by elemental analyses and 1H NMR. X-ray crystal structure of complex B reveals that the six-membered chelate ring adopts a envelope conformation, with nickel(II) atom deviating from the plane of backbone aromatic ring by 1.164 Å. In the presence of methylaluminoxane (MAO), both complexes showed moderate activities of 105 g molNi−1 h−1 for norbornene polymerization. β-iminoamine Ni(II)/MAO catalysts gave unimodal polymers (Mw, 3.16–8.02 × 105 g/mol) with a relatively narrow MWD (Mw/Mn, 1.59–2.14), indicative of single-site catalyst behavior. The obtained polymers are vinyl-type polynorbornenes (PNBs), which are soluble in common solvents such as toluene, cyclohexane and dichlorobenzene.

Graphical abstractβ-iminoamine ligands and Ni(II) complexes were synthesized and characterized. In the presence of MAO, β-iminoamine Ni(II) complexes were used as catalyst precursors for norbornene polymerization. β-iminoamine Ni(II)/MAO catalysts produce soluble vinylic polynorbornenes at an activity level of 105 g mol−1 h−1. The influences of temperature, Al/Ni ratios and precursor structure on polymerization behavior were examined.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Cationic Ni(II) complexes with six-membered chelate ring as catalyst precursors. ► Catalysts for vinyl addition polymerization of norbornene. ► Ni(II)/MAO produce vinylic polynorbornenes at 105 g mol−1 h−1 level. ► Unimodal and narrow MWD (1.59–2.14), indicative of single-site catalyst behavior. ► Sterically open precursors with nonplanar conformation are less active catalysts.