Catalyst Mileage in Olefin Polymerization: The Peculiar Role of Toluene

Abstract

Ti−C homolysis is generally regarded as a catalyst deactivation step in olefin polymerization catalyzed by titanium complexes. The present work demonstrates that for industrially relevant Ti catalysts in toluene and related solvents a "detour" via radical activation of the solvent can prolong catalyst lifetime and productivity, leading to chain transfer to solvents (CTS). For differently substituted phosphinimide half-titanocenes and other Ti catalyst classes, i.e. constrained geometry (CGC) and amidinate catalysts, CTS leads to formation of up to ∼60% benzylated chains. The efficiency of the reactivation pathway depends mostly on steric factors and correlates well with the percentage of buried volume, %V Bur , as well with as DFT predictors. Thus, the solvent is far from innocent, and catalyst behavior in such solvents may not be representative of polymerizations in more innocent saturated hydrocarbons. On the other hand, it might be the case that, in truly innocent solvents, the monomer itself can play a less innocent role.

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

“…Moving from these studies, we implemented a pool of seven descriptors, all related intuitively to simple electronic or steric properties of neutral LZrX 2 precatalysts that are easy to quantify with DFT methods ( Figure 4 and SI ) using previously established protocols (see experimental section for details) [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 ]. The six steric descriptors screen different regions of space around the catalyst, that were selected based on well-established olefin insertion and chain transfer transition state structures ( SI, Table S4 ).…”

“…Following the protocol proposed in Reference [ 65 ], all pre-catalysts were optimized at the TPSSTPSS/cc-pVDZ(-PP) [ 66 , 67 , 68 , 69 ] level of theory, using a small core pseudo potential on Zr [ 70 , 71 ]. The protocol has been successfully used, in combination with M06-2X [ 72 ] single-point energies (SP), to address several polymerization related problems: i.e., absolute barrier heights for propagation [ 73 ], comonomer reactivity ratios [ 74 , 75 ], metal-carbon bond strengths under polymerization conditions [ 76 , 77 , 78 ], electronic and steric tuning of M W capability [ 79 ], and QSAR modeling [ 13 ]. The density fitting approximation (Resolution of Identity, RI) [ 80 , 81 , 82 , 83 ] and standard Gaussian16 quality settings [Scf = Tight and Int(Grid = Fine)] were used throughout.…”

Separating Electronic from Steric Effects in Ethene/α-Olefin Copolymerization: A Case Study on Octahedral [ONNO] Zr-Catalysts

“…Trends in activity are generally difficult to rationalize, since they strongly depend not only on intrinsic barriers for chain propagation, but also on the percentage of active Zr-centers and catalyst decay mechanisms [10,72]. The amount of active metal is often relatively small [73,74], and difficult to determine [75]. Nevertheless, results in Table 1 are in line with general observation that the reactivity of cationic complexes increases with the electrophilicity of the metal center (vide infra) [76], although this can be affected by ion pairing effects in solution [77,78].…”

“…To unravel the connection between the catalyst structure and comonomer affinity, DFT studies have been carried out on complexes R 1 R 2 . The computational protocol (see Materials and Methods for details) has been previously benchmarked for group IV precatalysts and TSs relevant to olefin polymerization [54,74,[80][81][82], including specifically those for predicting reactivity ratios in copolymerization [33,39]. A facfac geometry for all complexes and TSs has been considered, which is generally accepted to be the most stable for the neutral complexes and the cationic active species; interconversion between active facfac and inactive mermer configurations of the naked cationic complex is generally assumed to represent a rapid pre-equilibrium with respect to chain propagation [43][44][45]83].…”

On the Nature of the Lewis Acidic Sites in “TMA‐Free” Phenol‐Modified Methylaluminoxane

“…[19,20,54,55] The Me/bht molar ratio of 9:1 found for the cages led to the tentative formula [AlOMe 0.9 (bht) 0.1 ] n . [20] Polymerization [39,45,[56][57][58][59][60][61][62][63] and spectroscopic [19,20] studies clearly indicate that the resulting modified MAO (MAO/BHT) effectively activates group IV precatalysts.…”