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.

Herein, we present a fundamental study of isostructural 2-methoxyethylamino-bis(phenolate)-lanthanide complexes [(ONOO)M(X)(THF)] (M = Lu, Y; R = Bu, CMePh, X = CHTMS, collidine; THF = tetrahydrofuran; TMS = trimethylsilyl) for rare-earth metal-mediated group-transfer polymerization (GTP). This analysis includes the differentiation of electron-donating and nondonating vinyl monomers and two metal centers with regard to the ionic radius (yttrium and lutetium). In addition, highly nucleophilic alkyl initiators are compared with electron-donating heteroaromatic initiators. Our examinations include the impact of these parameters on the activity, initiator efficiency, and tacticity of the obtained polymers. Density functional theory calculations and proposed catalyst structure determinations via X-ray analysis support these investigations. This facilitates the selection of the best metal and initiator combination to address efficient and stereospecific polymerization of a broad range of Michael monomers. [(ONOO)Lu(X)(THF)] shows the highest activity of 2220 h (normalized turnover frequency) for the polymerization of 2-vinylpyridine due to the higher Lewis-acidity of lutetium. Through C(sp)-H bond activation, catalysts with higher initiator efficiency in N,N'-dimethylacrylamide (DMAA) and diethylvinylphosphonate polymerization were synthesized. Remarkably, [(ONOO)Y(collidine)(THF)] was capable of stereospecifically polymerizing DMAA to highly isotactic poly(DMAA) (P = 0.94). Overall, the kinetics studies reveal a living-type GTP mechanism for all of the tested catalysts, enabling precise molecular-weight predeterminations with narrow molecular weight distributions (Đ ≤ 1.06).

Two novel silyl-bridged C 2 -symmetric 2-methyl-4-aryl-7-methoxysubstituted bis-indenyl-based titanocene complexes with varied steric demand (a, 4-(3′,5′-dimethyl)phenyl; b, 4-(3′,5′-di-tert-butyl)phenyl) were synthesized, characterized, and examined in the coordination polymerization of propene. Both adapted ligand structures have proven their capability as precise catalysts in the formation of stereodefect-and regiodefect-free isotactic polypropylene. Several activation pathways to the catalytically active, cationic complexes were analyzed in terms of catalytic activity and stability, taking into account the influence of polymerization temperature, monomer concentration, polymerization time, and type of applied scavenger. The overall lowest activities were observed using the methylaluminoxane (MAO) activated catalyst. The two-step activation mechanism of in situ alkylation with an excess of triisobutylaluminum (TIBA) and subsequent addition of [Ph 3 C][B(C 6 F 5 ) 4 ] resulted in moderate productivities of the respective catalyst systems. However, the highest catalytic activities were observed when eliminating the in situ alkylation step by application of bis-methylated titanocenes in combination with [Ph 3 C][B(C 6 F 5 ) 4 ]. The latter activation mechanism in combination with the sterically more encumbered ligand framework b results in the most productive titanium-based metallocene catalyst for the polymerization of propene to date, at least with respect to reasonable reaction times. The determined molecular weights of the produced polymers were significantly affected by the ligand structures a and b but were only negligibly influenced by the applied activation method. End-group analysis via 1 H NMR spectroscopy disclosed a chain release mechanism dominated by β-hydride elimination. In accordance with the observed accurate stereo-and regiocontrol mechanism, extraordinarily high melting transitions of up to 170 °C (ex reactor) underline the remarkable potential of these titanium-based catalyst systems in the polymerization of propene.

This contribution provides the first detailed analysis of the nature of the M–C σ-bond of three alkylated, isostructural group 4 (M = Ti, Zr, Hf) metallocenes, thereby elucidating individual peculiarities of each metal center in the catalytic conversion of olefins. Therefore, the subtle electronic differences of the individual M–C σ-bonds, which are considered crucial for several subprocesses in the coordinative polymerization of olefins, were examined by detailed experimental charge density studies. These studies provided measures of the increasing ionic character of the M–C bonds along the group 4 elements (Ti–C < Zr–C < Hf–C). These results are further supported by high-pressure diffraction studies showing that the predominantly ionic Hf–C bond is more compressible than the more covalent Zr–C bond in line with a smaller degree of electron localization in the valence shell of the hafnium relative to the zirconium atom along the M–C bond directions. The Ti–C bond displays the largest degree of electron localization in these group 4 metallocenes as witnessed by a pronounced bonded charge concentration in the valence shell of the titanium atom–a rare phenomenon in transition metal alkyls. All findings were then complemented by experimental and theoretical studies of the kinetic aspects of M–C σ-bond cleavage in group 4 metallocenes. These studies show that the entropy of activation is distinctly more negative for a Zr–C relative to a Hf–C bond dissociation. The combined results of the kinetic and electronic analysis herein shed new light on the different catalytic behavior of group 4 metallocenes with regard to the applied transition metal atom. In this context, deviations between zirconium- and hafnium-based catalysts concerning the catalytic activity and the stereoregularities became clearly explainable, just as the well-known “hafnium-effect” in the production of extraordinarily high molecular weight polypropylenes.

Provided is a concept of how the carbon content of CO/CO2-containing blast furnace gas (BFG) from steel production could be utilized in a sequence of selective chemical conversion steps to produce high value intermediates for the polymer industry.

Studies of polypropylene with different degrees of isotacticity have shown a way of the rational design of material with predetermined mechanical properties starting from the synthesis stage already-controlled introducement of stereodefects will allow the smooth adjustment of the Young's modulus and elasticity in the range from plastic to elastomer materials. It was also revealed that modern theoretical models of the elasticity can be successfully applied not only for the description of the mechanical behaviour of polymers, but also for better understanding of the mechanism of elasticity in them. While in the low crystalline materials deformation has Gaussian nature, in the materials of the intermediate crystallinity (30-40 %) percolation takes place, and the cross-linking network becomes harder, manifesting the switch to the thermotropic behavior of the material. Simultaneously the divide between cross-and sliplinks becomes substantial, as an extensibility grows sharply.

This contribution provides the simple one-pot, one-catalyst synthesis of high-melting (T m ∼ 140 °C), high-molecular-weight, elastic polypropylene ( e PP) offering an excellent reversible deformation behavior. The produced propylene-based thermoplastic elastomers contain of i PP– a PP block structures embedded in an amorphous polypropylene matrix which is enabled by the variable stereoselective behavior of ethylene-bridged fluorenylindenyl (EBFI) ansa-metallocene complexes. For the tailored synthesis of these high-melting e PPs the intricate interplay of various mechanisms, which collectively define the stereoregularity of the produced polypropylenes, was examined, and a decisive impact of different chelate ring conformers was elucidated. In this connection, the accurate adjustment of conformational interconversion with respect to the chain propagation and termination rate facilitated a directed switching between iso- and unselective polypropylene sequences in the catalytic production of highly temperature-stable, elastic polypropylene.

The ring opening polymerization of cyclic carbonates made from epoxide and CO2 to CO2-containing polymers constitutes an emerging technology of particular industrial interest. Considering the reaction of ring-opening polymerization of...