Reductive Decomposition of Cationic Half-Titanocene(IV) Complexes, Precursors of the Active Species in Syndiospecific Styrene Polymerization

Grassi, Alfonso; Zambelli, Adolfo; Laschi, Franco

doi:10.1021/om950666f

Cited by 149 publications

(89 citation statements)

References 23 publications

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“…Assignments of the resonances of the copolymer were carried out according to the previous reports. 8,18,[20][21][22][23][24][25] The spectrum of the insoluble part, obtained by TCE extraction of the crude product in Run 11, is shown in Figure 3. In addition to continuous homogeneous monomer sequences consisting of ethylene-ethylene (30.1 p.p.m.)…”

Section: Resultsmentioning

confidence: 99%

“…It has been traditionally believed that a trivalent titanium (Ti 3+ ) species is the predominant active species for the syndiotactic polymerization of styrene by the CpTiCl 3 /MAO type catalysts. [20][21][22][23][24][25][26] However, recent studies have indicated that a tetravalent titanium (Ti 4+ ) species is also generated and can similarly promote styrene polymerization in the CpTiCl 3 /MAO type catalyst system, independent of the Ti 3+ active species. [27][28][29][30][31] An analogous Ti 4+ species is believed to be the active species in olefin polymerization by metallocene-type catalyst systems (such as Cp 2 TiCl 2 /MAO).…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

Hagihara

Usui

Naga

2011

Polym J

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We describe the synthesis of a styrene-ethylene copolymer using a trivalent titanium-based polymerization catalyst system, tris(acetylacetonate)titanium (Ti(acac) 3 ), combined with triisobutylaluminum-modified methylaluminoxane. Gel-permeation chromatography measurement revealed that copolymerization using the above-mentioned catalyst system yielded a mixture of two different polymers. 13 C nuclear magnetic resonance (NMR) analysis of the Soxhlet-extracted fractions indicated that the insoluble part contained a long ethylene-ethylene sequence and an isolated styrene unit, whereas the soluble part contained a syndiotactic styrene-styrene sequence with ethylene units adjacent to continuous styrene units. The ratio of the styrene-styrene sequence to the styrene-ethylene joint part of the Soxhlet-soluble fraction, estimated from the NMR resonances, increased with the styrene content. The melting temperature of the Soxhlet-soluble fraction also increased with the (styrene-styrene)/ (styrene-ethylene) ratio of the polymers. These two results together indicate that a block-like copolymer was produced that contained long syndiotactic polystyrene portions separated by ethylene units.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

Hagihara

Usui

Naga

2011

Polym J

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“…11,12 To give a better insight into the effect of the residual TMA on the polymerization, oxidation state distributions of the Ti species were measured by redox titration. Ti oxidation states from the reactions of the titanocene with various MAOs are shown in Table I The results indicate that the residual TMA content in MAO can be correlated with the valent distribution of the Ti species in the catalyst systems.…”

Section: Polymerization With Various Maosmentioning

confidence: 99%

“…10 The com-plexes are not very stable in the presence of cocatalyst and monomer and tend to be reduced to lower oxidation states, for example, a trivalent Ti species, which is active for styrene polymerization. 11,12 In the previous article, 13 we have reported the styrene syndiotactic polymerization with monocyclopentadienyltitanium-MAO catalyst system and found that the residual TMA content in MAO influences the catalyst activity to a great extent.…”

Section: Introductionmentioning

confidence: 98%

Effects of residual and external alkylaluminum on the synthesis of syndiotactic polystyrene with cyclopentadienyltitanium tribenzyloxide-methylaluminoxane catalyst

Wu¹,

Gao²,

Lin³

1998

J. Appl. Polym. Sci.

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ABSTRACT:The effects of residual trimethylaluminum (TMA) in methylaluminoxane (MAO) and external alkylaluminum (AlR 3 ) on styrene syndiotactic polymerization with CpTi(OBz) 3 as a catalyst precursor have been investigated by comparison of the polymerizations using a series of MAOs containing various amounts of residual TMA. The results indicated that the residual TMA plays a deciding role in the reduction of Ti and promotes formation of the active centers for styrene polymerization. The variations in the catalytic activity and molecular weight of the polymer caused by additions of external AlR 3 , AlMe 3 , AlEt 3 , Al(i-Bu) 3 , and AlEt 2 Cl, into the catalyst systems are quite different, depending the properties of MAO used and the type of the external AlR 3 . It was found that there is an optimum range of concentration ratio of the free AlR 3 , including the residual TMA and external AlR 3 , to the total Al compounds, 25-35 mol %, for maximum catalytic activities. The catalytic activities decrease at the ratios either above or below the range.

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“…32 Thus, active sites originated under action of cocatalysts (MAO, perfluorophenyl borane, or borates) on mono-Cp titanium complexes, producing sPS, were Ti(III) species. [33][34][35]12 The Ti(IV) 3 Ti(III) reduction when MAO was added became evident even for silica-immobilized CpTiCl 3 . 36 The PE or E/S copolymer thus was formed on Ti(IV) cationic active centers.…”

Section: Introductionmentioning

confidence: 99%

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (M?Ti, X?CH3, M?Zr, X?iBu) in copolymerization of ethylene with styrene

Sukhova

Панин

Babkina

et al. 1999

J. Polym. Sci. A Polym. Chem.

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Catalytic activity of Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) [MTi, XCH3 (1); MZr, X=iBu (2)] systems in the ethylene/styrene (E/S) feed was examined. Experimental data revealed high activity for the catalytic system (1) for copolymerization ethylene with styrene, whereas the system with enhanced catalytic activity for ethylene homopolymerization (2) was temporarily blocked in the styrene presence yielding, even at high styrene content, homopolyethylene as the final product. Properties of thus obtained polymers were analyzed. Catalytic system (1) occurred very sensitive to S/E ratio in the comonomers feed. The 10‐fold acceleration for ethylene consumption was shown in two experimental sets conducted at S/E = 1.3 ratio, 1 bar, and 7.5 bar ethylene pressure, respectively. The consequent enhancement in S/E ratio resulted in slowing down both ethylene consumption and catalyst deactivation rates. Atactic polystyrene was formed at high styrene content with the catalyst (1). Catalytic system (1) allowed design of products with the highest styrene content (20 mol %) at low ethylene pressure, moderate temperature, and high S/E ratio. The apparent activation energy estimated from the initial rates of ethylene consumption was 54.6 kJ/mol. Analysis of apparent reactivity factors (rE = 9 and rS = 0.04; rE × rS = 0.4) and 13C‐NMR copolymer spectra revealed an alternating tendency of the comonomers for active center incorporation. DSC measurements showed considerable decrease of melting points and crystallinity even for copolymers with low styrene content. The catalyst produced relatively high–molecular weight copolymers (140–150 kg/mol) even at 80°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1083–1093, 1999

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Reductive Decomposition of Cationic Half-Titanocene(IV) Complexes, Precursors of the Active Species in Syndiospecific Styrene Polymerization

Cited by 149 publications

References 23 publications

Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

Effects of residual and external alkylaluminum on the synthesis of syndiotactic polystyrene with cyclopentadienyltitanium tribenzyloxide-methylaluminoxane catalyst

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (M?Ti, X?CH3, M?Zr, X?iBu) in copolymerization of ethylene with styrene

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