Metallocene methylene polymers

Monomeric vinylic metal n complexes undergo polymerisation reactions to form polymers that have limited applications because of their poor thermo-mechanical properties but they absorb UV without degrading in the process. Such polymers can be used as a UV-resistant coating and act as catalysts in other monomer reactions. Metallocene methylene polymers are high temperature resistant materials and have uses as ablative materials for space capsule heat shields. These materials use Fe and Ru in their metal polymers. 

Metallocene methylene polymers have also been prepared via the preparation of an a-metallocenylcarbocation with an acidic or Lewis acid initiator, followed by polycondensation involving electrophilic substitution of the metallocene nucleus... 

Metallocenes are far more versatile in controlling polymer stereochemistry compared to Ziegler-Natta catalysts, as extensively demonstrated in the case of PP. Also in 1-butene polymerization, all kinds of chain microstructures can be obtained with different metallocenes. The 13C NMR pentad analysis of polybutene is somewhat less immediate than that of PP, and has been reported for both ZN 886,887 and metallocenes.180 The 13C NMR spectrum of atactic polybutene, with pentad assignments of the C(3) methylene region, is shown in Figure 37. 

A new type of enantioselective diene polymerization is found with cyclopolymerization of 1,5-hexadiene which leads to polymers with a saturated chiral main chain28,58>109. As catalyst, (—)-(7 )-[l,T-ethylenebis(4,5,6,7-tetrahydro-l-indenyl)]zirconium (/ )-binaphtholate is used in the presence of methylalumoxane to give optically active poly(methylene-1,3-cyclopentane) (3) with 68% trans configuration in the five-membered ring (diisotacticity). If the (S)-enantiomer of the ansa-metallocene with (ft)-binaphthol is used as catalyst then the opposite rotation of the polymer is observed58. 

During the three decades following the discovery of ferrocene in 1951, the literature cited an extraordinarily large number of pubhcations in the area of polymeric ferrocene compounds, as scientists embarked on a search for new properties and applications of the metallocene that would be specifically associated with the polymer-bound, yet not with the monomeric, compound." " A special type of polymer used in space technology, a linear construct in which ferrocene nuclei are interconnected by simple methylene bridges," " represents just one example of these early endeavors. Whenever linear and essentially free from rotational restrictions, these polymeric, and quite lipophilic, ferrocenes were generally reported to possess solu-bihty in a restricted number of organic solvents, yet certainly not in water. 

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