Copolymerization of Ethylene with 1-Hexene and 1-Octene Catalyzed by Fluorenyl N-Heterocyclic Carbene Ligated Rare-Earth Metal Precursors
作者:Yao, CG,Wu, CJ,Wang, BL,Cui, DM
关键字:ziegler-natta catalysts; single-site catalysts; ethylene/1-hexene copolymerization; olefin polymerization; styrene polymerization; tandem action; cyclopentadienyl ligand; linked cyclopentadienyl; sequence distributions; branched polyethylene

Rare-earth metal bis(alkyl) complexes (Flu–NHC)Ln(CH2SiMe3)2 (Ln = Dy (1), Er (2), Sc (3)) attached by fluorenyl-modified N-heterocyclic carbene ligands ((Flu H–NHC–H)Br) have been synthesized by treatment of (FluH–NHC–H)Br with (trimethylsilylmethyl)lithium (LiCH2SiMe3) and rare-earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2) via double-deprotonation reactions in moderate to high yields. Under mild conditions (40 °C and normal ethylene pressure), the scandium precursor 3, upon activation of AliBu3 and [Ph3C][B(C6F5)4], showed high activity (4120 kg molSc–1 h–1 atm–1) for the copolymerization of ethylene and 1-hexene with moderate 1-hexene insertion ratio (20.2%), although the analogous complexes 1 and 2 were inert. In addition, this system displayed excellent catalytic performances for the copolymerization of ethylene and a higher α-olefin 1-octene with an activity of up to 3640 kg molSc–1 h–1 atm–1. The content of 1-octene could be controlled swiftly from 2.1% to 38.7% by varying the 1-octene feed ratio. Thus the isolated P(E-co-Oct) polymers varied from opaque crystalline solids with high melting points, e.g., Tm = 103.6 °C, to transparent elastomers. This represents the first rare-earth metal based homogeneous catalyst that can initiate the copolymerization of ethylene and 1-octene, the catalytic performances of which are comparable with those reported for the most active group 4 metallocene systems.