Polymerization of linear higher α-olefins with a modified Ziegler catalyst (original) (raw)
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Journal of Catalysis, 1964
A mechanism for the polymerization of olefins is proposed. An essentially octahedrally coordinated ion of a transition element with empty or nearly empty tzg orbitals carrying in its coordination sphere one alkyl group and having one vacant octahedral position is supposed to be the active center. In this model the monomeric olefin is coordin&ed in the vacant position through a 'Gr bond."
Ziegler-Natta catalysts for olefin polymerizations
Progress in Polymer Science, 1997
The current development of the metallocene-based Ziegler-Natta catalysts has been reviewed. The discovery of these catalysts has offered the opportunity to obtain a deeper insight into the mechanism of Ziegler-Natta polymerizations. In this review, some mechanistic models for polymerization and stereoregulation, as well as the factors which affect the activity and stereospecificity of the catalysts, have been discussed. The technology of olefin polymerization with the metallocene-based catalysts is in the early stage of commercialization. Using these catalysts, a large number of novel polymers with special properties have been obtained.
Ziegler-Natta catalysts for olefin polymerization: Mechanistic insights from metallocene systems
Progress in Polymer Science, 1995
The current development of the metallocene-based Ziegler-Natta catalysts has been reviewed. The discovery of these catalysts has offered the opportunity to obtain a deeper insight into the mechanism of Ziegler-Natta polymerizations. In this review, some mechanistic models for polymerization and stereoregulation, as well as the factors which affect the activity and stereospecificity of the catalysts, have been discussed. The technology of olefin polymerization with the metallocene-based catalysts is in the early stage of commercialization. Using these catalysts, a large number of novel polymers with special properties have been obtained.
Stereoselective polymerization of α-olefins by heterogeneous chiral Ziegler-Natta catalysts
Macromolecules, 1992
MgC12-supported Tic13 catalysts were synthesized to contain either chiral (racemic or optically active) or nonchiral Lewis basic esters. They were compared along with ordinary TiC13 in the stereospecific polymerization of propylene and in the stereoselective and stereoelective polymerizations of chiral 3-and 4-methyl-substituted olefins. The number and type of active sites, kinetic parameters, stereoregularity and optical purity of the polyolefins produced, and optical purity of unpolymerized monomer have been determined. The results suggest that active sites differing in steric constraints are responsible for the polymerizations of various monomers. The catalyst modified with the optically active Lewis base possesses several times more active centers of both stereospecific as well as nonstereospecific kinds than the catalyst modified with the corresponding racemic Lewis base in both propylene and racemic 4-methyl-l-hexene polymerizations. The results indicate a mechanism of site stereoselection by the chiral Lewis base. Polymerization of racemic 4-methyl-l-hexene, 3-methyl-l-hexene, and 3,7-dimethyl-l-octene by an optically active catalyst preferentially consumes one antipode showing stereoelectivity for the process.
A few considerations on some catalysts for olefin polymerization
Makromolekulare Chemie. Macromolecular Symposia, 1993
Among many precursors and catalysts for alpha‐olefins polymerization, one seems to be particularly interesting, because it has not been completely clarified yet.We refer especially to precursors obtained via reaction between Mg‐alkyls and SiCl4.The products of this reaction are not well known; in fact, under some operating conditions, a special form of MgCl2 is obtained, showing x‐ray diffraction peaks in the angular region lower than 15° (2 theta), which corresponds to the 5.9 A interplanar spacing, characteristic of alpha‐MgCl2.Under other conditions, MgCl2 is obtained in the well known and strongly disordered delta structure.By employing these precursors, some catalytic systems for alpha‐olefins polymerization have been prepared.In this paper, the peculiar aspects of these precursors and catalysts are described, particularly focusing on the correlation between structure and performances in ethylene and propylene polymerization.
A flat model approach to Ziegler-Natta olefin polymerization catalysts
2009
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Effect of monomer diffusion in the polymerization of olefins over Ziegler-Natta catalysts
1989
By using an extremely high stereospecific catalyst, three kinds of copolymerizations were carried out with combinations of monomers which differ in thecrystallinity of the homopolymers. Addition of a small quantity of comonomer to the homopolymerization systems producing very high crystalline polymers was found to cause a remarkable increase in the apparent polymerization rate as well as a marked decrease in the polymer crystallinity. Such an irregular increase in the polymerization activity was, however, not observed when a small amount of comonomer was added to the homopolymerization systems producing low-crystalline or amorphous polymers. These observations have led to the conclusion that resistance of monomer diffusion through the polymer film should be one of the significant parameters for the apparent polymerization rate when very high crystalline polymers, like high density polyethylene, isotactic polypropylene etc., are produced.