Retarded Anionic Polymerization, 5. Influence of the Structure of Dialkylmagnesium Additives on the Reactivity of Polystyryllithium Species

Ménoret, Stéphane; Carlotti, Stéphane; Fontanille, Michel; Deffieux, Alain; Desbois, Philippe; Schade, Christian; Schrepp, W.; Warzelhan, Volker

doi:10.1002/1521-3935(20011101)202:16<3219::aid-macp3219>3.0.co;2-m

Cited by 21 publications

(18 citation statements)

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“…For the (n,s-Bu 2 Mg) x /PBLi systems, results collected in Table 1 show that the polymerization rate and apparent propagation rate constant decrease drastically with increasing r (a factor of 260 from r ¼ 0 to 4). The experimental PB molar masses also decrease with increasing r, as previously reported for styrene [10][11][12] and butadiene polymerizations. [9] This behavior is in agreement with a co-initiation or a reversible chain transfer process For triisobutylaluminium-based systems, the butadiene polymerization rate and apparent propagation rate constant, shown in Table 2, also decrease drastically with increasing proportion of i Bu 3 Al (a factor of 330 from r ¼ 0 to 0.85).…”

Section: Buta-13-diene Polymerizationsupporting

confidence: 76%

“…[10][11][12][13] Much less data are available concerning diene polymerization. The kinetics of buta-1,3-diene polymerization initiated by PBLi seeds in the presence of the Lewis acid additives were investigated in cyclohexane at 40 8C using the dilatometry technique.…”

Section: Buta-13-diene Polymerizationmentioning

confidence: 99%

“…More recently, we have investigated in greater detail and over a much broader range the use of R 2 Mg (0 < [Mg]/[Li] ¼ 20) and of trialkylaluminium (R 3 Al) (0 < [Al]/[Li] < 1) as retarders of the styrene anionic polymerization initiated by alkyllithium derivatives at elevated temperature. [10][11][12][13] The formation of ''ate'' heterocomplexes between PSLi and the organometallic additives was found as the keystone for the retardation effect and the stabilization of active species at high temperature. However, the exact nature of the propagating species was not completely elucidated.…”

Section: Introductionmentioning

confidence: 99%

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Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives

Carlotti

Ménoret

Barabanova

et al. 2004

Macro Chemistry & Physics

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Summary: The influence of Lewis acid additives on the anionic butadiene polymerization using lithium as a counter ion in non‐polar solvent is investigated. A decrease of the polymerization rate was always observed. In the presence of n,s‐Bu2Mg the percentage of 1,2‐vinyl units increases with the [Mg]/[Li] ratio. This evolution can be explained by further complexation of lithium with free dialkylmagnesium modifying the nature of the propagating species and/or possible 1,4 to 1,2 isomerization during chain exchanges between lithium and magnesium derivatives. As a result of the transmetallation process, 0.5 to 1 supplementary chains are formed by magnesium depending on the [Mg]/[Li] ratio. In contrast, the iBu3Al/RLi system does not yield any modification of polybutadiene microstructure, which remains close to the one observed with s‐BuLi alone. The determination of the reactivity ratios in styrene‐butadiene copolymerization shows that tapered‐like copolymers are obtained in the presence of both n,s‐Bu2Mg and iBu3Al. However the magnesium derivative induces a lesser increase of styrene incorporation in the copolymer than the aluminium additive. The observed microstructure and reactivity ratios support that the monomer insertion proceeds directly into heterocomplexes.magnified image

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Section: Buta-13-diene Polymerizationsupporting

confidence: 76%

Section: Buta-13-diene Polymerizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives

Carlotti

Ménoret

Barabanova

et al. 2004

Macro Chemistry & Physics

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“…As already mentioned for α-olefins, the activity of the decamethylmetallocene RE / Mg system was observed as negligible for the insertion step of styrene in a polymerization catalytic cycle. Higher temperature gave effective chain transfer of oligostyrene on dialkylmagnesium, but with competitive radicalar and/or anionic mechanisms besides the coordination one [45][46][47][48]. By switching from Cp* to other ligands, a stereoselective CCTP process yielded near-perfect syndiospecific and isospecific oligostyrenes end-capped with magnesium [49][50][51].…”

Section: Styrenementioning

confidence: 99%

End-capped Oligomers of Ethylene, Olefins and Dienes, by means of Coordinative Chain Transfer Polymerization using Rare Earth Catalysts

Chenal¹,

Visseaux²

2014

Oligomerization of Chemical and Biological Compounds

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“…The reaction seems to be slower compared to the reaction studied by UV/Vis spectroscopy. The concentration is higher in the NMR study and magnesium compounds are known to form clusters [267,268] , which seems to mainly influence the reaction rate. The overall reaction rate for side product formation is notably high at 90 sidered negligibly small at 80 • C and below.…”

Section: Magnesium Based Co-catalystsmentioning

confidence: 97%

Mechanism and Kinetics of Catalyzed Chain Growth

Primpke¹

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In this work, the activation and polymerization mechanism of Catalyzed Chain Growth (CCG) polymerization of ethylene and styrene was studied. On the basis of two metallocene catalysts (Cp* 2 ZrCl 2 and Cp* 2 NdCl 2 Li(OEt 2 ) 2 ) and dibenzyl magnesium (BzMgBz) and n-butyloctyl magnesium (BuMgOct) as co-catalysts the mechanism was determined via a model reaction and afterwards transferred to a typical CCG system. The model system consisting of Cp* 2 ZrCl 2 and BzMgBz cannot perform β-hydride elimination and was first studied via Nuclear Magnetic Resonance (NMR). A mechanistic scheme was proposed and kinetic coefficients were successfully derived via modeling in PREDICI TM . Data analysis was simplified due to direct calculation of the coefficients from NMR data. The analytical toolbox was extended to Ultra-Violet/Visible (UV/Vis) spectroscopic studies. Based on this method the influence of di-n-butyl ether (DBE) on the catalyst/co-catalyst system was studied and a strong lowering of rate coefficients was found. The co-catalyst was switched to BuMgOct, where β-hydride elimination of the alkyl chains was found to be fast at 70 • C and dominating the activation mechanism. This hinders the system to perform ethylene polymerization. The UV/Vis method was applied to the reaction of Cp* 2 NdCl 2 Li(OEt 2 ) 2 with BzMgBz. Equilibrium constants between a monoalkylated complex and the benzyl brigded bimetallic Nd-Mg complex were determined in dependence of temperature. The reaction turned out to be strongly dependent on the presence of other coordinating molecules like DBE. The activation mechanism of Cp* 2 ZrCl 2 and BzMgBz was successfully utilized for modeling the polymerization of styrene-d8 by NMR studies. It was found that the basic steps of the exchange reactions are similar to those of activation. The model was successfully extended to the introduction of polymeric species, and kinetic parameters were derived. The process of monomer addition was found to be chain-length dependent and the influence of the single rate coefficients on the reaction were screened. It was found that a low catalyst precursor concentration can lead to a rate enhancement. Addition of tetrahydrofurane was found to be disadvantageous for the polymerization reaction. BuMgOct as co-catalyst leads to a process where the termination reaction of the alkyl Scheme 2.2: Transfer reaction scheme for magnesium derivatives. Adapted with permission from S. Bogaert et al. [21] Copyright 2000 WILEY-VCH Verlag GmbH, D-69451 WeinheimIn contrast to neodymium and iron-based catalysts, the chosen Cp * 2 ZrCl 2 (A)/ BzMgBz model system is non-paramagnetic. Initialization is a critical phase during polymerization in CCG. If the chains from the CTA are not transferred fast and the first monomer addition is slow the MMD will be broadened or the process goes over into a CCTP like polymerization. Results of this section were already published in literature [269] .

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Retarded Anionic Polymerization, 5. Influence of the Structure of Dialkylmagnesium Additives on the Reactivity of Polystyryllithium Species

Cited by 21 publications

References 2 publications

Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives

Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives

End-capped Oligomers of Ethylene, Olefins and Dienes, by means of Coordinative Chain Transfer Polymerization using Rare Earth Catalysts

Mechanism and Kinetics of Catalyzed Chain Growth

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