Side chains metallocene polymers

Through the addition of small amounts of propene, 1-butene, 1-hexene or 1-octene to ethylene, short side chains can be added to the main polymer chain. The word linear should be interpreted to mean the absence of chain branches. With these short side chains LLDPE has a density range from 0.900 g/cm3 for VLDPE (very LDPE) to 0.935 g/cm3 for octene-ethylene copolymer. In this field metallocene catalysts become more and more important. 

Interestingly, normal nonbridged metallocenes of zirconium with different chiral side chains or other chiral units, after activation with methylalumoxanes, also lead to stereoregular polymers with a pronounced effect of the different substituents48,95 -101. In terms of double stereodifferentiation, this is interpreted as proof of enantiomeric site control combined with the diastereo-control of the growing chain48. 

In general, much less work has been reported on side-chain polymers containing metallocenes other than ferrocene. For example, ruthenium and osmium analogues of poly(vinylferrocene) have been described, but their characterization has been fairly limited [16,42,43]. Poly(vinylruthenocene) is reported to be a light-yellow solid with a Tg>250°C, and the preparation of samples with molecular weights of up to... 

In the regular and real olefin polymerization processes with metallocene catalysts, the anion is an ever-present participant and an integral part of the functioning catalyst system. It is systematically displaced and moves (in and) out of the coordination sphere in a concerted action, while the monomer units approach for coordination to be paired again with the cation after the insertion process is complete. Assuming that the monomer approach proceeds along the most favorable path (i.e., via a cis approach with respect to the anion), immediately after the monomer insertion the anion is positioned at the outer coordination sphere, on the side of the polymer chain (Fig. 20a). 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

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