• Macromolecular Research
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• v.12 no.1
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• pp.100-106
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• 2004

We have prepared the polymethylene-bridged, dinuciear, half-sandwich constrained geometry catalysts (CGC)［Zr(η$\^$5/:η$^1$-C$\_$9/H$\_$5/SiMe$_2$NCMe$_3$)］$_2$［(CH$_2$)$\_$n/］［n=6(9), n=12(10)］by treating 2 equivalents of ZrCl$_4$with the corresponding tetralithium salts of the ligands in toluene. $^1$H and $\^$13/C NMR spectra of the synthesized complexes provide firm evidence for the anticipated dinuciear structure. In $^1$H NMR spectra, two singlets representing the methyl group protons bonded at the Si atom of the CGC are present at 0.88 and 0.64 ppm, which are considerably downfield positions relative to the shifts of 0.02 and 0.05 ppm of the corresponding ligands. To investigate the catalytic behavior of the prepared dinuciear catalysts, we conducted copolymerizations of ethylene and styrene in the presence of MMAO. The prime observation is that the two dinuclear CGCs 9 and 10 are not efficient for copo-lymerization, which definitely distinguishes them from the corresponding titanium-based dinuclear CGC. These species are active catalysts, however, for ethylene homopolymerization; the activity of catalyst 10, which contains a 12-methylene bridge, is larger than that of 9 (6-methylene bridge), which indicates that the presence of the longer bridge between the two active sites contributes more effectively to facilitate the polymerization activity of the dinuciear CGC. The activities increase as the polymerization temperature increases from 40 to 70$^{\circ}C$. On the other hand, the molecular weights of the polyethylenes are reduced when the polymerization temperature is increased. We observe that dinuciear metallocenes having different-length bridges give different polymerization results, which reconfirms the significant role that the nature of the bridging ligand has in controlling the polymerization properties of dinuclear catalysts.

• Macromolecular Research
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• v.9 no.2
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• pp.71-83
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• 2001

The metallocene compounds had been applied to the polymerizations of olefins and vinyl monomers with methylaluminoxane (MAO) cocatalyst, and they have usually one transition metal atom per molecule, i.e., mononuclear metallocene. Recently it has been found that the dinuclear metallocene compounds containing two transition metal atoms exhibit the peculiar polymerization behaviors for olefins and vinyl monomers. In this article, the dinuclear metallocenes are classified into four groups of dinuclear bent-metallocene, dinuclear ansa-metallocene, dinuclear constrained geometry catalyst and dinuclear half-metallocene, and then the synthesis of dinuclear metallocene of each group as well as the polymerization behaviors for ethylene, propylene, and styrene are described.

• Polymer(Korea)
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• v.35 no.1
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• pp.77-86
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• 2011

Polymerization properties of six dinuclear constrained geometry catalysts (DCGC) were investigated. The different length bridges of three catalysts were para-phenyl (Catalyst 1), para-xylyl (Catalyst 2), and para-diethylene phenyl (Catalyst 6). The other three DCGC have the same para-xylyl bridge with the different substituents at the phenyl ring of the bridge. The selected substituents were isopropyl (Catalyst 3), n-hexyl (Cataylst 4), and n-octyl (Catalyst 5), It was found that the longer catalyst not only exhibited a greater activity but also prepared a higher molecular weight copolymer. The catalyst 3 having a bulky isopropyl substituent revealed the lower activity but formed the highest molecular weight polymer comparing with the other alkyl substituted DCGCs. These results were able to be understood on the basis of the electronic and steric characteristics of the bridge. This study confirms that the control of the bridge structure of DCGC may contribute to control the microstructure of polymers.