2-Butene copolymerization, metallocene symmetry

Dependence on Metallocene Symmetry of E-Z Selectivity for 2-Butene Copolymerizations. We have seen in the Section 3.1.3 that opposite enantiofaces are favored for primary and secondary propene insertion on C2-symmetric metallocenes, whereas the same enantioface is favored for primary and secondary insertion on Cv-symmetric metallocenes. In this framework, if the same steric interactions which rule the enantioselectivity of primary and secondary propene insertions hold for 2-butene, the insertion of... 

As for olefins different from propene, molecular modeling studies have also been able to rationalize the dependence on metallocene symmetry of E-Z selectivity for 2-butene copolymerization as well as the stereoselectivity of the cyclization step, which determines the cis or trans configuration of the rings, for cyclopolymerization of nonconjugated dienes. 

In summary, the prediction that (E)-(Z) selectivity in the ethene/intemal olefins copolymerization with group 4 metallocenes can be achieved by using ligands of suitable symmetry has been proved. In particular, it has been shown that C2- and Os-symmetric metallocenes are able to copolymerize ethene with (Z)- and ( >butene, respectively. 

Propylene-1-butene and propylene-1-pentene copolymerization at 60°C in the propylene bulk with the homogeneous isospecific metallocene catalyst of the symmetry rac-Me2Si(4-Ph-2-MeInd)2ZrCl2 activated by methyl-aluminoxane is studied. Thermal, mechanical characteristics, and thermooxidation stability have been investigated. 

In this study, we examined the copolymerization of propylene with 1-butene and 1-pentene in liquid propylene medium in the presence of a highly active isospecific homogeneous a 5o-metallocene catalyst with the C -symmetry, rac-Me2Si(4-Ph-2-MeInd)2ZrCl2, activated by methyl-aluminoxane (MAO). The effects of the type of comonomer on the rate of copolymerization and the molecular mass characteristics, microstructure, thermophysical, and mechanical properties of the copolymers are investigated. The results of this study are compared with the data obtained with the same system used for the copolymerization of propylene with ethylene, 1-hexene, and l-octene. ... 

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