Recent Developments in the Determination of Active Centers in Olefin Polymerization

Mejzlík, Jiří; Vozka, Pavel; Kratochvíla, Ján; Lesná, Marie

doi:10.1007/978-3-642-83276-5_8

Cited by 5 publications

(3 citation statements)

References 27 publications

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“…A knowledge of the number of actual propagating centers, C*, is required so that the appropriate values for the rate constant for chain propagating, k p , may be calculated from the simplistic equation, R p = k p [C*][M]. There are some principal methods which are being used currently for the determination of active center concentrations in both heterogeneous and homogeneous Ziegler−Natta polymerization systems. , These analyses consist of (1) kinetic and molecular weight studies, (2) quenching methods, (3) radio-tagging procedures, and (4) simultaneous kinetic and adsorption methods.…”

Section: Introductionmentioning

confidence: 99%

“…There are some principal methods which are being used currently for the determination of active center concentrations in both heterogeneous and homogeneous Ziegler-Natta polymerization systems. 1,2 These analyses consist of (1) kinetic and molecular weight studies, (2) quenching methods, (3) radio-tagging procedures, and (4) simultaneous kinetic and adsorption methods.…”

Section: Introductionmentioning

confidence: 99%

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Determination of the Number of Active Sites for Olefin Polymerization Catalyzed over Metallocene/MAO Using the CO Inhibition Method

Han

Park

et al. 1996

Macromolecules

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For a determination of the active site concentrations, [C*], the simultaneous kinetics and inhibition method using CO as a catalyst inhibitor were examined. It is noticed that this evaluation method is not quantitatively exact because MAO-activated alkyl Zr sites exist in dynamic equilibrium between dormant states and a chain propagating site and because some CO molecules coordinate even to inactive species. The number of active sites was evaluated on the assumption that two molecules of CO coordinate to each active center. The increase in Al/Zr ratio and temperature increased both the number of active sites and the value of k p for ethylene polymerization over Cp2ZrCl2/MAO. Especially, a drastic increase of activity is mainly due to a much higher value of k p above a Al/Zr ratio of 2000. A comonomer enhanced drastically the catalytic activity to more than 10 times for ethylene−propylene copolymerization over the rac-Me2Si(Ind)2ZrCl2/MAO system. This is due to the drastic increase in the propagating rate constant, k p, rather than the increase in the formation of new active sites by the addition of comonomer.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Determination of the Number of Active Sites for Olefin Polymerization Catalyzed over Metallocene/MAO Using the CO Inhibition Method

Han

Park

et al. 1996

Macromolecules

View full text Add to dashboard Cite

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“…[C*] is usually determined from experiments in which the active sites are quenched (made inactive) with CH 3 O 3 H, 14 CO, or 14 CO 2 [Jaber and Fink, 1989;Mejzlik et al, 1986Mejzlik et al, , 1988Tait and Watkins, 1989;Vozka and Mejzlik, 1990]. Other methods include the use of number-average molecular weight (combined with polymer yield) and 14 C-labeled group I-III metal component.…”

Section: -4i-4 Values Of Kinetic Parametersmentioning

confidence: 99%

Stereochemistry of Polymerization

Odian

2004

Principles of Polymerization

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Constitutional (formerly: structural) isomerism is encountered when polymers have the same overall chemical composition (i.e., same molecular formula) but differ in connectivitythe order in which the atoms are connected to each other. Polyacetaldehyde, poly(ethylene oxide), and poly(vinyl alcohol) are constitutional isomers. The first two polymers are CH CH 3 O C H 2 CH OH CH 2 CH 2 O n n Polyacetaldehyde Poly(ethylene oxide) Poly(vinyl alcohol) n obtained from isomeric monomers, acetaldehyde and ethylene oxide. The third is obtained by hydrolysis of poly(vinyl acetate) since vinyl alcohol does not exist (it is the enol form of acetaldehyde). Poly(methyl methacrylate) and poly(ethyl acrylate) are isomeric polymers CH 2 C CH 3 CO 2 CH 3 CH 2 CH CO 2 C 2 H 5 n n Poly (methyl methacrylate) Poly (ethyl acrylate) formed from isomeric monomers. Poly(E-caprolactam) and poly(hexamethylene adipamide) are isomeric even though the monomers are not isomeric. Similarly, the 1 : 1 copolymer of Principles of Polymerization, Fourth Edition.

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Determination of the number of active centers in Ziegler‐Natta polymerization of propene using sulfur‐containing terminating agents 2. Tagging of growing chains during retardation of polymerization by carbon disulfide

Vozka

Mejzlík

1990

Makromol. Chem.

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The CS2-induced retardation of propene polymerization catalyzed by TiCl,/AIEt,Cl and TiCl,/ALEt, systems was investigated. From the two systems, the latter was much more active in polymerization and also exceedingly more susceptible to retardation by CS,. At least for the TiC1,/A1Et2C1-catalyzed polymerization, there is no diffusion limitation imposed on the reaction of growing chain with CS,. It was found that the number of sulfur tags introduced by the above CS, treatment is dominantly related to the ratio of polymerization rates before and after CS2 addition. Monomer plays a dual role during the CS, treatment: on one hand it enhances the CS, insertion into the growing metal-polymer bond, on the other hand it competes with CS2 in the same reaction. CS, reacts preferentially with centers of highest reactivity. It allows, in principle, the determination of the reactivity distribution of activecenters. Several potential side reactions which might lead to an increase of the number of tags in polymer were considered. None of the side reactions play an important role except for a reaction of CS, with chains formed via transfer with the organometal compound in AEt3-cocatalyzed polymerization.

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Recent Developments in the Determination of Active Centers in Olefin Polymerization

Cited by 5 publications

References 27 publications

Determination of the Number of Active Sites for Olefin Polymerization Catalyzed over Metallocene/MAO Using the CO Inhibition Method

Determination of the Number of Active Sites for Olefin Polymerization Catalyzed over Metallocene/MAO Using the CO Inhibition Method

Stereochemistry of Polymerization

Determination of the number of active centers in Ziegler‐Natta polymerization of propene using sulfur‐containing terminating agents 2. Tagging of growing chains during retardation of polymerization by carbon disulfide

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