High-Melting, Elastic Polypropylene: A One-Pot, One-Catalyst Strategy toward Propylene-Based Thermoplastic Elastomers

Machat, Martin R.; Lanzinger, Dominik; Drees, Markus; Altmann, Philipp J.; Herdtweck, Eberhardt; Rieger, Bernhard

doi:10.1021/acs.macromol.7b02679

Cited by 9 publications

(8 citation statements)

References 63 publications

(170 reference statements)

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“…The increase in temperature resulted in a greater degree of misinsertions; thus, the syndiotacticity decreased (Figures S28−S31). This behavior was consistent not only with an increased back-skip mechanism at an increasing temperature 37 but also through a general loss of stereocontrol. A difference in stereocontrol was observed when the central metal atom in Ia was changed to Hf.…”

Section: ■ Results and Discussionsupporting

confidence: 76%

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

et al. 2021

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Fluorenyl cyclopentadienyl C s -symmetric ansa-metallocene (M = Zr, Hf) complexes I−IV featuring different bridging motifs (C and Si) were synthesized and subsequently examined in the syndiospecific coordinative polymerization of propylene. All complexes were activated in situ with triisobutylaluminum (TIBA) and [Ph 3 C][B(C 6 F 5 ) 4 ] (TrBCF) in order to highlight the benefits of this in situ activation, resulting in a significantly higher molecular weight and a significantly increased productivity in comparison to methylaluminoxane (MAO). The isopropylidene-bridged zirconocene Ia (ZrCl 2 [Me 2 C(η 5 -Flu)(η 5 -Cp)]) exhibited a high productivity (80000 kg PP (mol cat h) −1 ) and stereoregularity ([rrrr] up to 93%) with a moderate molecular weight of polypropylene (PP), whereas the polymerization with the corresponding hafnocene Ib (HfCl 2 [Me 2 C(η 5 -Flu)(η 5 -Cp)]) resulted in a lower productivity and stereoregularity but yielded ultrahigh molecular weight polypropylene (M w = 1100 kg mol −1 ). The backbone in II (HfCl 2 [Ph 2 C(η 5 -Flu)(η 5 -Cp)]) was associated with a higher productivity and molecular weight, while the syndiotacticity was not affected. In contrast, SC-XRD revealed a reduced dihedral angle and D value for Si-bridged hafnocenes III (HfCl 2 [Me 2 Si(η 5 -Flu)(η 5 -Cp)]) and IV (HfCl 2 [Ph 2 Si(η 5 -Flu)(η 5 -Cp)]), resulting in a more constrained geometry of the catalyst. This led to an increased molecular weight, while the productivity as well as the syndiotacticity decreased due to these structural parameters. Activation of Ib and II−IV with n-octyl-modified methylaluminoxane (MMAO) resulted in a lower molecular weight of the polymer, because the transfer of the growing polymer chain onto the Al center was enhanced. Nevertheless, the stereoregularity of MMAO-activated catalysts was slightly increased, probably due to a coordination of the ill-defined MMAO anion during the polymerization. DSC analysis exposed for syndiotactic polypropylene (sPP) produced by the highly active zirconocene Ia a defined melting transition (T m up to 145.2 °C), whereas TIBA/TrBCF-activated hafnocenes Ib and II−IV gave polymers with no observable T m value.

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Section: ■ Results and Discussionsupporting

confidence: 76%

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

et al. 2021

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“…Today, zirconocene complexes are commonly stated to be the most active ones in the polymerization of propene, whereupon examples are known in which suitably activated hafnocenes exhibit comparably high activities. − This is contrary to previous reports assigning the lower activities of Hf to lower chain propagation rates as a result of a stronger metal–carbon bond. ,, In contrast, the catalytic activity of titanocene complexes generally suffers from catalyst deactivation due to reductive processes. ,, The exchange from Zr to Hf becomes particularly important regarding the molecular weights of the respective polymers. Significantly higher molar masses for the polymers of the hafnocene compared to the zirconocene analog are herein observed for C 1 -, C 2 - and C s -symmetric ansa -metallocene complexes and have established the so-called “hafnium effect”. ,,,, In this context, a stronger Hf–C versus Zr–C bond has served as most plausible explanation for more than three decades. ,,, However, the impact of a thermodynamically more stable bond on the molecular weight of the produced polymer chains is not directly related since kinetics finally determine the averaged chain lengths of a polymer. Accordingly, it is the rate ratio of chain propagation and chain release that gives the respective molecular weights and evokes the elementary question how the M–C bond strength favors the propagation relative to the chain release reactions.…”

Section: Introductionmentioning

confidence: 83%

“…Significantly higher molar masses for the polymers of the hafnocene compared to the zirconocene analog are herein observed for C 1 -, C 2 -and C ssymmetric ansa-metallocene complexes and have established the so-called "hafnium effect". 12,14,18,21,22 In this context, a stronger Hf−C versus Zr−C bond has served as most plausible explanation for more than three decades. 8,12,18,23 However, the impact of a thermodynamically more stable bond on the molecular weight of the produced polymer chains is not directly related since kinetics finally determine the averaged chain lengths of a polymer.…”

Section: ■ Introductionmentioning

confidence: 99%

Behind the Scenes of Group 4 Metallocene Catalysis: Examination of the Metal–Carbon Bond

Machat¹,

Fischer

Schmitz

et al. 2018

Organometallics

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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.

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“…Among them, homogeneous vanadium catalysts are of great importance. These catalytic systems are derived from a combination of vanadium compounds (e.g., VCl 4 , VOCl 3 , VO(OR) 3 , V(acac) 3 , R = alkyl group, acac = acetylacetonate) and alkyl aluminum halide (typically Et 2 AlCl) or aluminum hydride derivatives, and a Lewis base (e.g., anisole). 29−34 Herein, we report the terpolymerization of ethylene with propylene and ENB catalyzed by known imido vanadium(IV) complexes, 35,36 differing in the ligand substitution, in combination with Et 2 AlCl and Cl 3 CCO 2 Et (ETA).…”

Section: Introductionmentioning

confidence: 99%

Semibatch Terpolymerization of Ethylene, Propylene, and 5-Ethylidene-2-norbornene: Heterogeneous High-Ethylene EPDM Thermoplastic Elastomers

Leone¹,

Zanchin²,

Girolamo

et al. 2020

Macromolecules

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Thermoplastic elastomers (TPEs) are materials combining the processability of thermoplastics and the elasticity of rubbers. The global value and demand of TPEs is expected to grow in coming years, and advancement in synthetic chemistry is the key driving force. This contribution provides a simple synthesis of high−ethylene EPDMs with high molecular weight, narrow molecular weight distribution (1.9 < M w /M n < 2.3), and properties which can be adjusted from soft thermoplastic to elastomer. EPDMs are prepared through the terpolymerization of ethylene with propylene and 5ethylidene-2-norbornene (ENB), where ethylene is continuously supplied to the reaction bath, while 2 propylene and ENB are added only at the beginning. Polymerizations are catalyzed by three known imido vanadium(IV), differing in the imido substituents and coligand, in combination with Et 2 AlCl and Cl 3 CCO 2 Et. The obtained EPDMs are a mixture of macromolecules each of them featuring a non random comonomer distribution, and non uniform composition. Each chain likely contains multiblocks where the comonomers are segmented, i.e., blocks with high ethylene content that may crystallize, and blocks with high propylene and ENB content that may not crystallize. This broad chemical composition distribution is due to time drift that occurs during the polymerization, which in turn depends on the experimental conditions and ligand set. Composition drift causes variation in the instantaneous feed comonomer ratio, and hence in the chemical composition of the terpolymer over the period of conversion. In proper experimental conditions, EPDMs behave as TPEs without the need of vulcanization, polymer blending, and reinforcement through the addition of fillers. They exhibit high elongation at break, strain hardening at large deformation, remarkable shape retention properties (up to 76% recovery after 10 cycles at 300%, and about 90% at 410% strain), and remelting processability with no fall in properties for recycle and reuse.atmosphere for 8 h, distilled, and stored over 5Å molecular sieves away from bright light. Ethyltrichloroacetate (ETA, Aldrich, 97%) was dried by stirring over CaH 2 for about 4 h, and then distilled under reduced pressure. Et 2 AlCl (Aldrich) was used as received. ENB (Aldrich, mixture of endo and exo, 99% pure), 1-hexene (Aldrich, 97% pure), and 1-octene (Aldrich, 98% pure) were dried by stirring over CaH 2 for about 4 h, then distilled under reduced pressure and, finally, stored under dry nitrogen and kept at -30 °C. The synthesis of imido V(IV) complexes, hereinafter referred as 1a, 2a and 2b, is reported in our previous work. 35,36 Polymerization Experiment. Polymerizations were carried out in a 100 mL roundbottomed Schlenk flask containing a stirring bar. Prior to starting polymerization, the reactor was heated to 110 °C under vacuum for 1 h, and backfilled with nitrogen. The typical reaction procedure for ethylene/propylene/ENB terpolymerization is as follows. Toluene, the appropriate amount of propylene (as a toluene solution), ENB, ...

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High-Melting, Elastic Polypropylene: A One-Pot, One-Catalyst Strategy toward Propylene-Based Thermoplastic Elastomers

Cited by 9 publications

References 63 publications

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

Behind the Scenes of Group 4 Metallocene Catalysis: Examination of the Metal–Carbon Bond

Semibatch Terpolymerization of Ethylene, Propylene, and 5-Ethylidene-2-norbornene: Heterogeneous High-Ethylene EPDM Thermoplastic Elastomers

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