Metallocenes nonconjugated dienes

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. 

Cyclopolymerization. As discussed earlier, nonconjugated dienes can be polymerized with metallocene-based catalysts to afford cyclopol5miers. In contrast to linear polyolefins which have only two microstructures of maximum order (isotactic and syndiotactic), cyclic polymers have four microstructures due to the possibility of configurational isomerism (cis vs trans) in the main chain (Fig. 16). Of these the frares-diisotactic structure contains no mirror planes of S5unmetry and is chiral by virtue of its main-chain stereochemistry (481). Two criteria for chirality of this microstructure are the presence of trans rings and isotacticity (the same... 

FIGURE 19.2 Various metallocene and half-metallocene catalyst precursors for the cyclo(co)polymeiization of nonconjugated dienes. 

Copolymerizations of ethylene and/or propylene with nonconjugated dienes using various metallocene catalysts are a useful method to synthesize polyolefins with cyclic backbones. 

Polyolefins with cyclic units in the backbone show high TgS and high transparencies, and thus are suitable for optical and medical applications." " Even though they can be prepared by the copolymerization of ethylene and cyclic olefins (such as norbomene) using metallocene catalysts, the cyclopolymerization of nonconjugated dienes offers another access route into cyclopolymer materials. 

Naga, N. Shiono, T. Ikeda, T. Copolymerization of propene and nonconjugated diene involving intramolecular cychzation with metallocene/methyl aluminoxane. Macromolecules 1999, 32, 1348-1355. 

The typical group IV metallocenes have been applied to the polymerization of nonconjugated dienes with great success. Reviews of the zirconocene-mediated cydopolymetization of linear a,co-dienes thoroughly explain the detailed... 

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