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Ethylene/1,3-butadiene cyclocopolymerization catalyzed by zirconocene systems
No full textCopolymerizations of ethylene with 1,3-butadiene in the presence of catalytic systems based
on C2-symmetric zirconocenes rac-(CH3)2Si(2-R-4-R0-1-indenyl)2ZrCl2 (where R = CH3– or H
and R0 = C6H5– or H) are compared. The chemical nature and the relative amount of constitutional
comonomer units from butadiene (1,4-trans, methylene-1,2-cyclopentane and
methylene-1,2-cyclopropane) are strongly affected by the bulkiness of the substituent on
the indenyl ligands. The unsubstituted indenyl zirconocene system rac-(CH3)2Si(indenyl)2-
ZrCl2/methylalumoxane (MAO) inserts 1,3-butadiene leading to both cyclopentane and
1,4-trans units, whereas exclusively cyclopentane constitutional units are obtained from
rac-(CH3)2Si(2-methyl-1-indenyl)2ZrCl2/MAO. The catalytic system rac-(CH3)2Si(2-methyl-
4-phenyl-1-indenyl)2ZrCl2/(MAO) is able to incorporate about 30% of butadiene units into
polymer chains and to form up to 10% of cyclopropane units. An unusual insertion mechanism
for conjugated diolefins, that involves a butadiene g2 primary coordination and insertion
leading to formation of cycloalkane units, is largely predominant for all used catalytic
systems. Mechanistic studies and DFT calculations indicate that the chemoselectivity of
the reaction depends on the bulkiness of the substituents on the indenyl ligands of catalyst
Solvent effect in 1,3-butadiene polymerization by cyclopentadienyl titanium trichloride (CpTiCl3)/methylaluminoxane (MAO) and pentamethylcyclopentadienyl titanium trichloride (Cp*TiCl3)/MAO catalysts
No full textStereospecific cis-1,4 polymerization of 1,3 butadiene is carried out by using CpTiCl3/MAO and Cp*TiCl3/MAO
catalysts in solvents (mesitylene, toluene, benzene, chlorobenzene, m-chlorobenzene, hexafluorobenzene)
having different nucleophilicity. The influence of nucleophilicity of used solvent on activity and selectivity of the
two considered catalytic systems is evaluated. Catalyst activity is strongly affected by used solvent, while
polymer microstructure remains almost unchanged. The formation of a labile specie anti-η3-π-butenyl-Ti coordinated
to solvent molecule, able to increase the rate of polymerization reaction, is hypothesized. The effect of
two different external electron donors, N(C2H5)3 and P(C6H5)3, in the polymerization environment on activity
and selectivity of the two considered catalytic systems is also investigated. Both N(C2H5)3 and P(C6H5)3 induce a
sweeping decrease of catalyst activity, but do not cause changes in polymer microstructures
Polimerizzazioni di fenil-1,3-butadieni utilizzando sistemi catalitici di tipo Ziegler-Natta
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Stereospecific polymerization of substituted butadienes in the presence of C2 symmetric ansa-zircocenes
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