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Polyolefins are unique among synthetic polymers because their wide application envelope originates from a finely controlled microstructure of hydrocarbon chains, lacking any distinctive functional groups. This hampers the methods of automated sorting based on vibrational spectroscopies and calls for much more complex 13 C NMR elucidations. High-temperature cryoprobes have dramatically shortened the acquisition time of 13 C NMR spectra, and few minutes are now enough for polyolefin classification purposes; however, conventional data analysis remains labor and time-consuming. In this paper, we introduce an instrument for automated fast determinations of the 13 C NMR microstructure on polyolefin materials, implemented by integrating High-Throughput Experimentation and Data Science tools and methods. From the scientific standpoint, the main interest of the approach is the solution proposed to address the general problem how to rapidly characterize statistically distributed analytes, of which synthetic polymers are a most important case. In practical terms, the instrument represents the first automated tool for microstructural polyolefin analysis: it is readily applicable to monomaterials, whereas extension to multimaterials, including postconsumer streams, is feasible but still requires some work.

Group 4 metallocenes are competent catalysts for the oligomerization of higher α-olefins. Among the many chemical and physical variables of importance in the process, one is the choice of cocatalyst (activator). The impact of various activators on the performance of a representative catalyst, (nBuCp) 2 ZrCl 2 , in the oligomerization of 1-octene was thoroughly investigated; in particular, the molecular weight distribution (MWD) of the oligomers was determined by means of high-resolution high performance liquid chromatography (HR-HPLC). Unexpectedly, a bimodal MWD was highlighted when the precatalyst was activated with methylaluminoxane (MAO), whereas a single Schulz-Flory (SF) MWD was observed with borate salts. The presence of Al centers with different Lewis acidity in the complex and ill-defined structure of MAO is well known, and the broadening effects on the MWD of olefin polymerization products made with metallocene/MAO catalyst systems have been reported before. However, to the best of our knowledge, clear HR-HPLC evidence of two active species resulting from activation with MAO of one single zirconocene precursor, yielding two discrete SF product distributions, is unprecedented. By varying the polarity of the reaction medium, we managed to modulate the MWD of the oligomers from bimodal to monomodal, even with MAO, thus demonstrating that ion pairing effects are behind these unusual findings.

A set of metallocene olefin polymerization catalysts bearing triptycene moieties in either position 4-5 (complexes Ty1-Ty5) or in position 5-6 (complexes Ty6-Ty8) of the basic dimethylsilyl-bridged bis(indenyl) system has been tested in propene polymerization and in ethene/1-hexene copolymerization. Comparison of the results with QSPR (quantitative structure-property relationship) predictions not parametrized for these exotic ligand variations demonstrates that trends can still be identified by extrapolation. Interestingly, Ty7, upon suitable activation, provides a highly isotactic polypropylene with an exceptional amount of 2,1 regio-errors (8%). The previously developed QSPR type models successfully predicted the low regioselectivity of this catalyst, despite the fact that the catalyst structure differs significantly from the benchmark set.

Hafnium catalysts for olefin polymerization are often very sensitive to the nature of cocatalysts, especially if they contain "free" aluminium trialkyls. Herein, cocatalyst effects in Hf-catalysed propene polymerization are examined for four Hf catalysts belonging to the family of C S -symmetric (Hf-CS-Met) and C 2 -symmetric (Hf-C2-Met) metallocenes, as well as of octahedral (Hf-OOOO) and pentacoordinated (Hf-PyAm) "post-metallocenes". The performance of the recently developed {[iBu 2 (PhNMe 2 )Al] 2 (μ-H)} + [B(C 6 F 5 ) 4 ] - (AlHAl) cocatalyst is compared with that of established systems like methylalumoxane, phenol-modified methylalumoxane and trityl borate/tri-iso-butylaluminium. The worst catalytic performance is observed with MAO. Conversely, the best cocatalyst varies depending on the Hf catalyst used and the performance indicator of interest, highlighting the complexity and importance of selecting the right precatalyst/cocatalyst combination. AlHAl proved to be a suitable system for all catalysts tested and, in some cases, it provides the best performance in terms of productivity ( e.g. with hafnocenes). Furthermore, it generally leads to high molecular weight polymers, also with catalysts enabling easy chain transfer to Al like Hf-PyAm. This suggests that AlHAl has a low tendency to form heterodinuclear adducts with the cationic active species, therefore preventing the formation of dormant sites and/or termination events by chain transfer to Al.

Group 4 metal-Salan olefin polymerization catalysts typically have relatively low activity, being slowed down by a pre-equilibrium favoring a non-polymerization active resting state identified as a mer-mer isomer (MM); formation of the polymerization active fac-fac species (FF) requires isomerization. We now show that the chemistry is more subtle than previously realized. Salan variations bearing large, flat substituents can achieve very high activity, and we ascribe this to the stabilization of the FF isomer, which becomes lower in energy than MM. Detailed in situ NMR studies of a fast ( o -anthracenyl) and a slow ( o - t Bu) Salan precursors, suitably activated, indicate that preferred isomers in solution are different: the fast catalyst prefers FF while the slow catalyst prefers a highly distorted MM geometry. Crystal structures of the activated o -anthracenyl substituted complex with a moderately (chlorobenzene) and, more importantly, a weakly coordinating solvent (toluene) in the first coordination sphere emphasize that the active FF isomer is preferred, at least for the benzyl species. Site epimerization (SE) barriers for the fast catalyst (Δ S > 0, dissociative) and the slow catalyst (Δ S < 0, associative) in toluene corroborate the solvent role. Diagnostic NMe 13 C chemical shift differences allow unambiguous detection of FF or MM geometries for seven activated catalysts in different solvents, highlighting the role of solvent coordination strength and bulkiness of the ortho -substituent on the isomer equilibrium. For the first time, active polymeryl species of Zr-Salan catalysts were speciated. The slow catalyst is effectively trapped in the inactive MM state, as previously suggested. Direct observation of fast catalysts is hampered by their high reactivity, but the product of the first 1-hexene insertion maintains its FF geometry.

The dinuclear aluminum salt {[ i Bu 2 (DMA)Al] 2 ( μ -H)} + [B(C 6 F 5 ) 4 ] - ( AlHAl ; DMA = N , N -dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues for tailoring the activator to specific needs. We report here, as proof of concept, a first variant ( s-AlHAl ) bearing p -hexadecyl- N , N -dimethylaniline (DMA C16 ) units, which enhances solubility in aliphatic hydrocarbons. The novel s-AlHAl was used successfully as an activator/scavenger in ethylene/1-hexene copolymerization in a high-temperature solution process., Competing Interests: The authors declare no conflict of interest.

Efficient and economical plastic waste upcycling relies on the development of catalysts capable of polymer degradation. A systematic high-throughput screening of twenty-eight polymerization catalyst precursors, belonging to the catalyst families of metallocenes, ansa-metallocenes, and hemi- and post-metallocenes, in cis-1,4-polybutadiene (PB) degradation reveals, for the first time, important structure-activity correlations. The upcycling conditions involve activation of the catalysts (at 0.18 % catalyst loading) with tri-iso-butyl aluminum at 50 °C in toluene. The data indicate the ability to degrade PB is a general reactivity profile of neutral group 4 metal hydrides. A simple quantitative-structure activity relationship (QSAR) model utilizing two descriptors for the distribution of steric bulk in the active pocket and one measuring the metal ion electrophilicity reveals the degradation ability improves with increased but not overbearing steric congestion and lower electrophilicity., (© 2022 Wiley-VCH GmbH.)