Preparation of highly branched polyolefins by controlled chain‐walking olefin polymerization

Abstract

A series of α‐diimine nickel(II) catalysts bearing different para‐substituted groups, {[(4‐R‐2,6‐Me2‐C6H2NC)2Nap]NiBr2, Nap: 1,8‐naphthdiyl; R = CHMePh (C1); R = CHPh2 (C2); R = tBu (C3); R = Br (C4); R = Me (C5)}, were synthesized and characterized. The molecular structures of C1 and C3 were determined by single crystal X‐ray analysis and show distorted tetrahedron geometry with C2v symmetry. The catalytic behaviors of these catalysts toward ethylene polymerization were investigated in the presence of diethylaluminum chloride (Et2AlCl) as a cocatalyst. The fast chain‐walking process in N,N‐chelated nickel system can be efficiently modulated via the introduction of para‐sec‐phenethyl substituents with improved thermal stability and catalytic performance. C1‐Et2AlCl exhibited high thermal stabilities and high activities reaching 4.61 × 106 g PE (mol Ni h)−1, producing highly branched amorphous polyethylenes (up to 143 branches/1000C) with high molecular weight and narrow polydispersity. This catalyst system conducted successfully conducted 2‐octene polymerization in comparison with the corresponding 1‐octene polymerization. The result demonstrated 2‐octene polymerized slower than 1‐octene and produced the highly‐branched poly(2‐octene)s with approximately 120 branches/1000C, including methyl, ethyl, amyl, and hexyl branches and a small amount of the long methylene sequence due to monomer isomerization.

Chain‐walking polymerization of ethylene and 1‐octene with ortho‐phenyl‐based α‐diimine Ni (II) catalysts

“…55 The reduction in polymer branching density is attributed to the inhibition of chain-walking process from the perspective of polymerization mechanism (Scheme 1,I). The microstructure of the highly branched PE produced by C2-Et 2 AlCl at 80 C (Figure 5; entry 12, Table 1), data collected by 13 C NMR characterization 56,57 showed the presence of 70 methyl, 7 ethyl, 3 propyl, 2 n-butyl, 1 sec-butyl, and 22 longer chains (the number of carbon atom larger than 4, Scheme 1,I).…”

Investigations of aryl substituents electronic effects in the catalytic behavior of thermostable α‐diimine nickel (II) catalyst on ethylene polymerization

“…Although electronic effects can significantly influence the properties of the produced polymer through the design of new catalysts with new features, they have received less attention than steric effects. Reports in the literature suggest the electronic properties of the catalyst affect the polymer topology, which is probably due to the change in the relative rate constants for monomer insertion and chain walking ( k ins / k walking ) 22–25,29 . Also, modifying the catalytic system by adjusting the electronic properties through changing the ligand substituents can influence the Lewis acidity of the metal as well as the σ‐donating ability of the ligand to metal center 30,31 .…”

“…Reports in the literature suggest the electronic properties of the catalyst affect the polymer topology, which is probably due to the change in the relative rate constants for monomer insertion and chain walking (k ins /k walking ). [22][23][24][25]29 Also, modifying the catalytic system by adjusting the electronic properties through changing the ligand substituents can influence the Lewis acidity of the metal as well as the σ-donating ability of the ligand to metal center. 30,31 The presence of electron-donating groups on the ligand structure afforded a higher lifetime and thermal stability for the catalysts.…”

From tetramerization to oligomerization/polymerization of ethylene by dinuclear pyridyl‐imine Co‐ and Ni‐based catalysts

“…[4][5][6] On the other way, there are many reports on late transition metal (LTM) complexes as an interesting class of catalysts due to feasibly preparation and modification, capability of production of a wide range of polyethylene/oligoethylene, intriguing and unusual behavior (e.g., chain-walking olefin polymerization). 1,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Multinuclear LTM catalysts along with their mononuclear analogs are widely used for preparation of ethylene homopolymers/copolymers and oligomers. [22][23][24] In the most cases, not only higher catalytic activity has been observed but also metal-metal cooperative effect in terms of greater selectivity in products has been reported.…”