Alkyl-and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,Ndimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium systems Li[C 5 H 4 -CR 1 R 2 NMe 2 ]. Subsequent treatment with ZrCl 4 ‚2THF gives the corresponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium to give the (C 5 H 4 CR 1 R 2 NMe 2 ) 2 Zr(CH 3 ) 2 complexes 11a (R 1 ) R 1 ) CH 3 ) and 11b (R 1 ) CH 3 , R 2 ) Ph), respectively. Treatment of 11 with tris(pentafluorophenyl)borane was carried out to generate the corresponding alkylmetallocene cations (12), which turned out to be unstable under the reaction conditions applied (-20°C) with regard to liberation of 1 equiv of methane by CH activation at a methyl group adjacent to nitrogen and formation of the spiro-metallocene complex systems 13. CH activation may be a major reaction pathway open to alkylzirconocene cation systems under suitable reaction conditions.
The opposing effects of activation enthalpy and entropy most likely cause the transition from isotactic via atactic to syndiotactic polypropylene in polymerizations with the soluble metallocene catalyst 1 (X Ph) and methylalumoxane when the reaction temperature is increased from −50 to +10°C. This proves how important temperature considerations are for structure–reactivity discussions.
The Spherizone process technology, which is based on a multizone circulating reactor (MZCR), represents a significant innovation in polypropylene (PP) production. In comparison to traditional multi-step technologies, the MZCR provides a step change in the polymer homogeneity of the final product, obtained by continuously circulating the growing polymeric granules between two interrelated zones where different gas-phase compositions are realized. In addition to traditional Z-N catalysts, metallocene catalysts are also being introduced in PP manufacture: single-site catalysts allow differentiated products with outstanding property combinations. Due to its versatility and sustainability, PP continues to be utilized in a large range of applications. Innovative polymer structures featuring diverse comonomers exhibit improved properties (i.e., stiffness-impact balance, aesthetics, transparency, processability), which reinforce the capability of PP to replace traditional materials such as wood, paper, glass, and metals, as well as standard polymer products.
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