Mechanistische untersuchungen der propenpolymerisation mit dem katalytischen system [2,4-cyclcopentadien-1-yliden(methylethyliden)1H-inden-1-yliden]zirkoniumdichlorid-methylaluminoxan

Ethene−Norbornene Copolymerization Using Homogenous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 2. Comparative Study of Different Metallocene- and Half-Sandwich/Methylaluminoxane Catalysts and Analysis of the Copolymers by 13C Nuclear Magnetic Resonance Spectroscopy

“…Conforming to these circumstances, the norbornene insertion is not favored by one of the two possible conformations and the insertion of the norbornene proceeds from both coordination sites, which enables the formation of longer norbornene microblocks in the copolymer and during the homopolymerization process of norbornene. The mainly isotactic structure of the norbornene blocks in the copolymer shows that it is not the symmetry of the metallocene which is decisive but the relative energy differences between the possible conformation minima with re - or si -coordinated olefin as shown by Fink et al in the case of propene homopolymerization. , …”

“…The mainly isotactic structure of the norbornene blocks in the copolymer shows that it is not the symmetry of the metallocene which is decisive but the relative energy differences between the possible conformation minima with re-or si-coordinated olefin as shown by Fink et al in the case of propene homopolymerization. 28,29 A different situation occurs when a tert-butyl group is introduced: Ethene-norbornene copolymers that are produced by i Pr[(3-t Bu-Cp)Ind]ZrCl 2 contain meso-connected norbornene microblocks with a maximum length of two and the norbornene homopolymerization activity is nearly zero. The insertion of norbornene is restricted on both sides of the metallocene, due to the larger sterical demands of the tert-butyl group.…”

Syndiospecific Propylene Polymerization Using C1-Symmetric ansa-Metallocene Catalysts: Substituent and Bridge Effects

“…C 1 -symmetric metallocenes containing bridged indenyl and cyclopentadienyl ligands are, as a class, not very active for propylene polymerization. ,,− Nevertheless, some of these metallocenes yield polypropylenes of intermediate to low isotacticity with interesting elastomeric properties. The range of isotacticities observed for polypropylenes obtained from these metallocenes has been interpreted in terms of the insertion of propylene into a stereoselective and nonstereoselective site in competition with the migration of the polymer chain from one site to the other …”

Syndiospecific Propylene Polymerization with C1 Symmetric Group 4 ansa-Metallocene Catalysts

“…The nature of the 3-indenyl substituent appears to be a critical factor of the stereospecificity exhibited by catalysts derived from metallocenes 3 − 7 . Chien reported that the 3-methyl-substituted analogue Me 2 C(Cp)(3-MeInd)ZrCl 2 ( 17 ) yields hemiisotactic polypropylene; the unsubstituted derivatives Me 2 C(Cp)(Ind)MCl 2 ( 16 ) are known to give atactic, hemiisotactic, or isotactic/atactic stereoblock polypropylenes depending on the polymerization conditions. ,− ,,, These results have been rationalized by positing that C 1 symmetric metallocenes typified by 16 and 17 possess one isospecific and one aspecific site; strictly alternating insertion at each site produces hemiisotactic polypropylene, and multiple insertions at a given site yield either atactic or stereoblock polypropylenes depending on the relative rate of insertion vs site isomerization. ,, …”

“…Chien reported that the 3-methyl-substituted analogue Me 2 C-(Cp)(3-MeInd)ZrCl 2 (17) yields hemiisotactic polypropylene; 12 the unsubstituted derivatives Me 2 C(Cp)-(Ind)MCl 2 (16) are known to give atactic, hemiisotactic, or isotactic/atactic stereoblock polypropylenes depending on the polymerization conditions. 12,[23][24][25]33,62,63 These results have been rationalized by positing that C 1 symmetric metallocenes typified by 16 and 17 possess one isospecific and one aspecific site; strictly alternating insertion at each site produces hemiisotactic polypropylene, and multiple insertions at a given site yield either atactic or stereoblock polypropylenes depending on the relative rate of insertion vs site isomerization. 12,25,33 Our experiments demonstrate that bridged cyclopentadienyl-3-R-indenylmetallocenes substituted by an ethyl (3) or a trimethylsilylmethyl (4) group generate syndiospecific polypropylene.…”