Perfectly Isotactic Polypropylene upon In Situ Activation of Ultrarigid meso Hafnocenes. Issue 46 (17th October 2022)

• Record Type: Journal Article
• Authors: Stieglitz, Lucas; Lenz, Tim M.; Saurwein, Andreas; Rieger, Bernhard
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 46(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-17
• Subjects: Activation -- Hafnocenes -- Isomerization -- Isotactic Polypropylene -- Metallocenes; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202210797
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: For more than 40 years, the synthesis of C 2 ‐symmetric indenyl‐based racemic metallocenes for the isoselective polymerization of propylene relied on a tedious separation of the produced rac and meso isomers. Status quo, latter are considered wasteful as they produce atactic polypropylene (aPP) rather than isotactic polypropylene (iPP) if activated with methylaluminoxane (MAO). Unexpectedly, the in situ activation of meso hafnocene I yielded perfectly isotactic polypropylene. We verified an isomerization of the meso compound to the corresponding racemic one upon triisobutylaluminum (TIBA) addition via nuclear magnetic resonance (NMR) spectroscopy and established an easy and convenient polymerization protocol, enabling productivities comparable to pure rac ‐I if applied to pure meso ‐I or a mixture of both isomers. With this established isomerization protocol, the potential yield of iPP was enhanced by more than 400 %. This protocol was also shown to be applicable to other meso hafnocenes and some initial mechanistic insights were received. Abstract : Using in situ activation, hafnocene meso‐ I yields isotactic polypropylene instead of atactic polypropylene of meso ‐I and rac ‐I . With our easy and convenient isomerization and polymerization protocol, productivities comparable to pure rac ‐I if applied to pure meso ‐I or a mixture of both isomers are accessible.