α-Diimino-nickel(II) and palladium(II) complexes are highly active in the (co)polymerization of ethylene, α-olefin and polar monomer and produce high molecular weight polymer. Recently, a series of α-diiminonickel complexes with bulky dibenzhydryl substituted groups has been designed and synthesized by Linlin Fan, a graduate co-supervised by associate professor Cun-Yue Guo and professor Wen-Hua Sun. Taking advantage of the electronic and steric effect of substituted groups on ligands, these novel complexes were used for ethylene polymerization with methylaluminoxane (MAO) the co-catalyst. These nickel complex catalytic systems were very active (1.27 × 107 g PE (mol of Ni)−1 h−1, 30 ºC) and the as-prepared polyethylenes were found to possess high molecular weight (up to 1.62 × 106 g mol−1), narrow molecular weight distribution (~ 2.0), and high branching degree (up to 202/1000C) (Fig. 1). This work is published in Journal of Polymer Science, Part A: Polymer Chemistry (http://onlinelibrary.wiley.com/doi/10.1002/pola.27572/epdf).
Fig. 1 Ethylene polymerization to highly branched polyethylene.
Based on the above-mentioned results, further modified 1-(2,4-dibenzhydryl-6-chlorophenylimino)-2-aryliminoacenaphthyl nickel complexes were synthesized and exhibited good thermo-stability towards ethylene polymerization (Fig. 2). Upon activation with inexpensive co-catalyst ethylaluminum sesquichloride (EASC) at low Al/Ni molar ratio, these nickel complexes showed high ethylene polymerization activities up to 1.09 × 107 g PE (mol of Ni)−1 h−1 (50 ºC), (3.76 × 106 g PE (mol of Ni)−1 h−1even at 80 ºC, producing branched polyethylenes in which the portion of long branches was significantly increased. This work is published in RSC Advances (http://pubs.rsc.org/en/content/articlepdf/2015/ra/c5ra18257c).
The work is supported by NSFC (51373176).