Control of molecular weight distribution for polypropylene obtained by commercial Ziegler–Natta catalyst: effect of temperature

Zhang, Hexin; Lee, Young‐joo; Park, Joon-Ryeo; Lee, Dong‐Ho; Yoon, Keun‐Byoung

doi:10.1007/s00289-011-0472-5

Cited by 15 publications

(6 citation statements)

References 20 publications

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“…Modification in such Cp-ligand structures leads to a significant change in the polymer properties. The single-site catalyst "metallocene" 13 typically produces a narrow molecular weight distribution in comparison to the multisite Ziegler−Natta catalyst 14 system, which basically generates the multimodel/ broad molecular weight distribution. However, few studies 15 have also reported the multimodality behaviors in alkyl-substituted Cp-ligand metallocenes.…”

Section: ■ Introductionmentioning

confidence: 99%

Single to Multiple Site Behavior of Metallocenes through C–H Activation for Olefin Polymerization: A Mechanistic Insight from DFT

Kumawat

Gupta

2019

ACS Catal.

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Density functional theory has been used to study single to multiple site behavior of metallocene catalysts for olefin polymerization using (Cp Pr ) 2 Hf(R) 2 and (Cp Pr ) 2 Zr(R) 2 (here, R = Me and n-butyl group) and boron activators B(C 6 F 5 ) 3 and [CPh 3 ] + [B(C 6 F 5 ) 4 ] − . Detailed pathways were investigated for two steps: (i) catalyst activation and (ii) ethylene and 1-hexene polymerization. For the catalyst activation step, the C−H activation of Cp-substituents (here, the n-propyl group) has also been studied, which leads to another active site named "metal cyclic active site" in comparison to the conventional active site. Among these sites, the formation of a metal cyclic active site is slower with respect to the conventional active site. Additionally, two different routes have been explored for the catalyst activation, depending on the nature of activators, and observed that [CPh 3 ] + [B(C 6 F 5 ) 4 ] − is a better activator with respect to B(C 6 F 5 ) 3 . Moreover, complete insertion (primary and secondary) and termination (chain transfer to monomer and β-H elimination) steps have also been studied for both the active sites. These results suggest that the metal cyclic active site can also produce the ethylene and 1-hexene polymer, which defines the multiple site behavior of metallocene catalysts, which explains the broadening of molecular weight distribution of linear low-density polyethylene-produced metallocene catalysts. Along with hafnocene and zirconocene, the toluene-solvated hafnocene catalyst system has also been investigated for catalyst activation and ethylene polymerization for comparison study. These results indicate that the toluene-solvated hafnocene catalyst system is energetically more facile in comparison to other catalysts. Furthermore, the effect of solvents as well as dispersion interaction on catalyst activation steps has been studied for the (Cp Pr ) 2 M(n-butyl) 2 (M = Hf and Zr) catalyst systems and observed that the dispersion interaction played an important role in the catalyst activation process. In addition to this, the regio-and stereoselective behavior of 1-hexene monomer for the (Cp Pr ) 2 Hf(Me) 2 catalyst has been investigated, and it was found that the metal cyclic active site improves the stereoselective nature of the hafnocene catalyst. Therefore, the current chemical calculations provide insights into the nature of active sites in metallocene catalysts for olefin polymerization.

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Section: ■ Introductionmentioning

confidence: 99%

Single to Multiple Site Behavior of Metallocenes through C–H Activation for Olefin Polymerization: A Mechanistic Insight from DFT

Kumawat

Gupta

2019

ACS Catal.

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“…The deconvoluted GPC curves cleared that the number of active centers decreases from 7 to 5 and 9 to 7 in PH and PO, respectively in the presence of the CMMS. It can justify the reduction in PDIs, clearly . Furthermore, focusing on deconvoluted GPC curves in Figure , one can deduce that adding silane external donor affected both high molecular weight and low molecular weight species in a different manner.…”

Section: Resultsmentioning

confidence: 87%

Effects of monomer length on α‐olefins polymerization using a conventional Ziegler–Natta catalyst

et al. 2018

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α-Olefin monomers with different lengths from C 4 to C 10 were polymerized via a conventional Ziegler-Natta catalyst. It was found that activity of the catalyst decreases with increase in the monomer length as well as introduction of external donor. GPC results exhibited a steady decrease in molecular weight from poly1butene to poly1-decene; however, PDI did not show a clear trend. Based on differential scanning calorimetry and X-ray diffraction analyses, poly1-butene and poly1-decene represented crystalline structure with one and two melting points, respectively, while poly1-hexene and poly1-octene showed amorphous nature. The content of isotactic pentads increased from poly1-butene to poly1-octene, with maximum value of mmmm = 76%, but decreased again in poly1-decene. Calculated ΔE re-si values showed a peak by increasing monomer length which was in line with the experimental results for isotactic content. K E Y W O R D S

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“…The trend of hydrogen concentration effect on polypropylene molecular weight was also found in Kissin 43 and Zhang. 44 3.1.5 Effect of scale-up. Generally, the purpose of reactor scaling up is to increase the production rate with the same product quality i.e.…”

Section: Results Based On Phenomenological Modelmentioning

confidence: 99%

“…The trend of hydrogen concentration effect on polypropylene molecular weight was also found in Kissin 43 and Zhang. 44 …”

Section: Resultsmentioning

confidence: 99%

Heat transfer effect in scaling-up a fluidized bed reactor for propylene polymerization

et al. 2018

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Control of molecular weight distribution for polypropylene obtained by commercial Ziegler–Natta catalyst: effect of temperature

Cited by 15 publications

References 20 publications

Single to Multiple Site Behavior of Metallocenes through C–H Activation for Olefin Polymerization: A Mechanistic Insight from DFT

Single to Multiple Site Behavior of Metallocenes through C–H Activation for Olefin Polymerization: A Mechanistic Insight from DFT

Effects of monomer length on α‐olefins polymerization using a conventional Ziegler–Natta catalyst

Heat transfer effect in scaling-up a fluidized bed reactor for propylene polymerization

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