Ultrarigid Indenyl-based Hafnocene Complexes for the Highly Isoselective Polymerization of Propene: Tunable Polymerization Performance Adopting Various Sterically Demanding 4-Aryl Substituents

Abstract

Two novel silyl-bridged C 2 -symmetric (2-methyl-4-aryl-7methoxy) substituted bisindenyl based ansa-hafnocene complexes of varied steric demand (I, II,-phenyl]) were synthesized and examined in the coordinative polymerization of propene. Both complexes enable a comparative study with the state of the art homogeneous metallocene catalyst (III, 4-[(3′,5′-tert-butyl)-phenyl]) for high melting ultrahigh molecular weight isotactic polypropylene. All three activated complexes exhibit extremely concise stereoregularity along with high molecular weights and high melting transitions at low to moderate polymerization temperatures. Increased sterical encumbrance of the 4-aryl substituent prevents the process of chain release reactions more effectively, especially due to enhanced reduction of β-methyl elimination. Accordingly, end group analysis disclosed the highest selectivity toward allylic chain ends as a result of β-methyl elimination with the less sterically encumbered complex I. Examination of the catalytic activity of I−III disclosed considerable impact of the varied 4-aryl substituents on the maximum productivity with respect to the applied polymerization conditions considering the combined influence of activation, monomer diffusion rate, catalyst deactivation, and rate of chain growth.

From elastomers to thermoplasts – Precise control of isotactic propylene structure and properties and the role of different structural elements in its mechanical behaviour

“…Especially the latter aroused huge interest, since this polymer class is not accessible using classic Ziegler-Natta type systems [21,22,23] C1 symmetric complexes based on an ethylene-bridged fluorenyl-indenyl ligand framework (metallocene catalyst M) already demonstrated their high potential in polymer catalysis from elastic to thermoplastic polypropylene [6,24,25,26]. Approaches to isotactic polypropylene are generally conducted using heterogenic Ziegler-Natta type catalysts, although metallocene systems are nowadays available exceeding the heterogeneous ones in terms of stereo-and regioregularity as well as the potential to catalyze ultra-high molecular weights [27,28].…”

An Integrated High Throughput Experimentation/Predictive QSAR Modeling Approach to ansa-Zirconocene Catalysts for Isotactic Polypropylene

“…Finally, a 7-methoxy substituent ( M29 ) increases stereoselectivity when compared to the same substituent pattern without it ( M14 ). Rieger et al have argued on the basis of crystal structure analysis that: (a) the stereorigidity imparted by said methoxy substituent leads to lower values of ligand bite angle (α) [ 93 ] and Ph-Ind dihedral angle (β), and (b) this would be beneficial for the stereoselectivity (higher indeed for M29 compared with M2 ) [ 94 ]. Gas phase DFT structures of a series of homologous precatalysts actually paint a different picture, and show that stereoselectivity primarily increases with increasing β ( Table 2 ).…”

Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

“…On the other hand, for the series of C 2 -symmetric silicon-bridged ansa-bis(indenyl) or {SBI}-metallocene catalysts, significant breakthroughs have been achieved in the last decade, and a number of new structures have emerged that exhibit significantly improved performances (Scheme 1). Among them, of note are metallocene catalysts A [13][14][15][16] and B [17] that bear bulky aromatic 4-indenyl substituents and afford astonishing productivities, with highly crystalline iPP having remarkably low amounts of stereo-and regioerrors. Very recently, zirconocene catalyst C, which incorporates conformationally rigid tripticenyl…”