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February 1998
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6 Reads
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5 Citations
Journal of Molecular Catalysis A Chemical
Four newly synthesized bridged bisindenyl zirconocenes which are derivatives of known structures have been tested in polymerizations of liquid propylene with methylaluminoxane as cocatalyst. They include two asymmetric and two binuclear systems which are suitable for isotactic polymerization. Surprising differences from the behavior of similar systems (regiospecificity, chain termination) are found and discussed.
February 1998
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2 Reads
Muanyag Es Gumi/Plastics and Rubber
February 1998
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4 Reads
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54 Citations
Journal of Molecular Catalysis A Chemical
Four newly synthesized bridged bisindenyl zirconocenes which are derivatives of known structures have been tested in polymerizations of liquid propylene with methylaluminoxane as cocatalyst. They include two asymmetric and two binuclear systems which are suitable for isotactic polymerization. Surprising differences from the behavior of similar systems (regiospecificity, chain termination) are found and discussed.
November 1997
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5 Reads
Journal of Molecular Catalysis A Chemical
The invention relates to a metallocene compound of the formula I ##STR1## where the two indenyl ligands have substitution patterns different from one another. The metallocene compound can be used as catalyst component for olefin polymerization.
January 1995
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10 Reads
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41 Citations
Chiral bridged bisindenyl zirconoeenes with special substitution patterns on the aromatic rings are potentially commercial catalysts for the production of isotactic polypropylenes. The performance characteristics of these systems are different, the variations being induced by size and position of the substituents. The novel catalysts will be used for the production of new iPP grades with enhanced properties or unprecedented property combinations. Typical features of metailocene iPP polymers are higher stiffness, higher transparency, and a lower level of extractables than conventional products. The most recent new designs of metailocene PP catalysts are discussed. These include asymmetric systems and metallocenes inducing two-step-polymerization mechanisms.
January 1995
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10 Reads
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44 Citations
Macromolecular Symposia
Structure-performance relationships in the propene polymerization behaviour of a number of silicon bridged bisindenyl zirconocenes show a rational pattern. Prognosis of the polymerization behaviour of different type structures, however, often fails, which is demonstrated by three examples of new zirconocenes. These include two bisindenyl complexes with two-membered silicon bridges and one isospecific bridged fluorenyl cyclopentadienyl species. It is thus demonstrated that the scope of a “rational catalyst design” in the field of metallocene catalysts is still limited.
March 1994
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15 Reads
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615 Citations
Organometallics
The synthesis of seven new bridged zirconocenes is described, which make isotactic polypropylene when used in polymerizations of propylene with methylaluminoxane as cocatalyst. Their polymerization behavior in propylene and ethylene polymerizations is examined and discussed. Aromatic substituents in appropriate positions of the zirconocene ligand frame result in catalysts with activities, stereospecificities, and polypropylene molecular weights much higher than those of any previously described metallocene system. By structure variations it is demonstrated that the effectiveness of these substitutions strongly depends on their position and on a nonincremental synergism with alkyl substituents on the ligand frame. The high activities of the systems can be explained well by electronic effects, whereas steric effects obviously play the more important role for the high stereospecificities and high molecular weights of the polymers.
October 1992
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17 Reads
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96 Citations
Angewandte Chemie
October 1992
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29 Reads
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329 Citations
A breakthrough for the technical application of zirconium catalysts in isotactic propylene polymerization has been achieved with complexes 1. The highest molecular mass of polypropylene, the best isotacticity, and the highest activity of all catalysts are provided by 1, R1 = R3 = CH3, R2 = i-C3H7. Hydrogenation of the six-membered ring drastically lowers the activity and the molecular mass obtained.
January 1992
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19 Reads
Angewandte Chemie
Polypropylene having isotacticities 94-98% and mol. wt. (32-46) × 103 was prepd. using I (R1 = H, Me, Et; R2 = H, Pr-iso; R3 = Me,Ph) or II (R1 = H, Me, Et) in combination with methylaluminoxanes as catalysts. [on SciFinder(R)]
... The authors have cited additional references within the Supporting Information. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] ...
November 1989
... Regarding propylene polymerization, both highly isotactic [6] and highly syndiotactic [7] polymers have been synthesized, as well as almost all microstructures in between [1][2][3][4][5][6][7][8][9][10][11]. Moreover, differences in the stereo-and regioregularity of propylene units allow for the fine adjustment of polymer microstructure and properties. ...
October 1992
... The interest in this area has primarily been driven by the potential to exploit intermetallic cooperativity/synergism between the two or more proximal metal centers to eventually enhance the performance of polymerization systems. For instance, several studies on dinuclear catalysts suggest that catalyst activity [3][4][5][6][7][8][9][10][11][12][13] and molecular weight, [3,7,10,14] tacticity, [13][14][15], or comonomer incorporation [8,[16][17][18][19][20] of/in the resulting polymers the existence of pairs of diastereoisomers in each case, and also of their different tautomers (i.e., isomers of C=C bonds within the CpH rings). The ESI-MS measurements data showed clearly the expected molecular [M + H] + ions at m/z 815.55, 787.52 for 2a,b and at 853.51 ([M + K] + ) for 2c. ...
February 1998
Journal of Molecular Catalysis A Chemical
... Graphene nanoplates were obtained by chemical or thermal reduction of graphite oxide [26]. Graphite oxide was obtained by the modified Hummers method, i.e., graphite oxidation with KMnO 4 in concentrated sulfuric acid. ...
March 1994
Organometallics
... As illustrated in Table 1.14, sPPs, produced by SSC metallocene catalysts, show a higher level of irregularities than iPP. With the same degree of tacticity, the syndiotactic polymer exhibits a lower melting point, lower density, lower crystallinity, and lower crystallization rate [185,186]. The smaller crystal size in sPP enables a higher clarity of the material but is also responsible for its inferior gas barrier properties, limiting its utility in food packaging applications. ...
Reference:
Polyolefins
August 1991
Macromolecular Symposia
... Comparing different metallocene catalysts, zirconocene catalysts are more active than titanocene and the classical Ziegler-Natta catalysts by around 10-100 times. 16,17 Moreover, titanocene catalysts cannot be used at high temperature and for long polymerization times, because the titanium(IV) will be then reduced to the inactive titanium(III). 18 In addition, hafnocene catalysts are about 10 times less active than titanocene catalysts, but they do produce polyethylene with a higher molecular weight. ...
January 1995
Macromolecular Symposia
... The interest in this area has primarily been driven by the potential to exploit intermetallic cooperativity/synergism between the two or more proximal metal centers to eventually enhance the performance of polymerization systems. For instance, several studies on dinuclear catalysts suggest that catalyst activity [3][4][5][6][7][8][9][10][11][12][13] and molecular weight, [3,7,10,14] tacticity, [13][14][15], or comonomer incorporation [8,[16][17][18][19][20] of/in the resulting polymers Catalysts 2018, 8, x FOR PEER REVIEW 3 of 19 Scheme 2. Synthesis of the para-and meta-phenylene-bridged bis(fulvenes) 1a-c. ...
February 1998
Journal of Molecular Catalysis A Chemical
