Syndiospecific Polymerization Of Styrene Research Articles

Syndiospecific polymerization of styrene using fluorinated indenyltitanium complexes

Nine new fluorinated half-sandwich titanocene complexes (1b-9b) based on substituted alkylindenes were synthesized, by reacting Me 3 SnF with the corresponding chloride species, and employed as catalyst precursors for the syndiospecific polymerization of styrene. When activated with methylaluminoxane (MAO), the new precursors 1b-9b exhibited increased activities by factors of 15-40 compared with the corresponding chlorinated compounds and provided improved syndiotacticity, enhanced melting temperature, and higher polymer molecular weights. The activities of indenyl and methyl- or phenyl-substituted indenyl complexes were found to be higher by factors of 4-12.5 than those of CpTiF 3 and Cp * TiF 3 . More importantly, the amount of MAOcan be reduced to an Al: Ti molar ratio of 300 in the temperature range of 10-90°C. It is likely that Ti-F, more polarized than the Ti-Cl bond in the half-sandwich titanocenes, allows the formation of more active and stable active sites of Ti(III) complexes needed for the syndiospecific polymerization of styrene. Evidence in this direction is brought via the electron paramagnetic resonance (EPR) spectrum and redox titration. The higher activity and syndiospecificity of the fluorinated catalysts are attributable to a greater number, more stable Ti(III) active sites, and/or higher propagation rate constant.

Syndiospecific polymerization of styrene using fluorinated indenyltitanium complexes

Syndiospecific polymerization of styrene using fluorinated indenyltitanium complexes

Improvement of supported catalysts for syndiotactic polymerization of styrene

The catalytic system Ti(OBu) 4 in combination with methylaluminoxane (MAO) was tested for the syndiospecific polymerization of styrene. A comparison was established between this homogeneous catalytic system and the same one supported on silica or alumina. An attempt was made to introduce a tether between the support and the active species to enhance both productivity and syndiospecificity. These tethers consisted of diols with different lengths. At last, the catalytic system Zr(OBu) 4 was supported on silica or alumina with MAO as a cocatalyst and was tested under the same conditions as other catalysts. This study reveals that Ti(OBu) 4 supported on silica enhances the productivity and leads to higher molecular weights, while the addition of a diol does not result in any enhancement compared to the silica-supported catalyst. On the contrary, alumina alone does not seem to be a good support for Ti(OBu) 4 , while introducing a short diol such as ethylene glycol leads to a great enhancement of both productivity and syndiospecificity. As reported in the literature, Zr(OBu) 4 always leads to much lower productivities than Ti(OBu) 4 .

Syndiospecific polymerization of styrene: Activity enhancement of Ti/MAO catalytic systems in the presence of SnR4 compounds

Syndiospecific polymerization of styrene: Activity enhancement of Ti/MAO catalytic systems in the presence of SnR4 compounds

Syndiospecific polymerization of styrene: Activity enhancement of Ti/MAO catalytic systems in the presence of SnR4 compounds

Syndiospecific polymerization of styrene: Activity enhancement of Ti/MAO catalytic systems in the presence of SnR4 compounds

ESR study on MgCl2-supported half-titanocene catalyst for syndiospecific polymerization of styrene

Abstract The MgCl2-supported CpTiCl3 catalysts with different Ti content were prepared and used for syndiospecific polymerization of styrene. These catalysts were investigated by means of electron spinning resonance (ESR) spectroscopy. It is found that there exist two kinds of active species in this catalytic system. One is a specific active site and cannot be removed into the solution by MAO. The other one is readily removed into the solution during the interaction with MAO, and the same active site as that in the CpTiCl3-MAO homogeneous system is formed. The MgCl2 supported CpTiCl3 catalyst was also compared with the SiO2/CpTiCl3-MAO system. The data show that the CpTiCl3 supported on the MgCl2 surface is more difficult to be removed by MAO than the active site immobilized on the SiO2 surface, leading to the lower activity of MgCl2/CpTiCl3-MAO system and lower syndiotacticity of obtained polystyrene.

(Pentamethylcyclopentadienyl)titanatrane: A New Class of Catalyst for Syndiospecific Polymerization of Styrene

A new type of catalyst for the syndiospecific polymerization of styrene, Cp*Ti(N(CH2CH2O)3) (3), was prepared by either the reaction of triethanolamine with Cp*TiCl3 in the presence of triethylamine or the reaction of (N(CH2CH2O)3)TiCl with LiCp*. The former reaction route is more efficient in terms of yield and easy accessibility of a titanium starting compound. The X-ray analysis reveals that 3 exists in a monomeric form in the solid state and the Ti atom adopts essentially an η5 bonding posture with regard to the Cp* ring and a tetradentate bonding mode with regard to the triethanolateamine ligand via a transannular interaction from the bridgehead N atom to Ti. The compound 3, which is stable to air and heat and soluble in hydrocarbon solvents, shows very efficient catalytic activity for the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as cocatalyst.

Reactivity of the [(η5-C5Me5)TiCH3][RB(C6F5)3] Complexes Identified as Active Species in Syndiospecific Styrene Polymerization

The reactivity of the alkyl complexes [Cp*Ti(III)(CH3)][RB(C6F5)3] (Cp* = η5-C5Me5; R = CH3, −C6F5) with α-13C-enriched p-chlorostyrene has been investigated by means of ESR spectroscopy in order to gain insight into the chemical structure of the active species in syndiospecific polymerization of styrene and substituted styrenes promoted by “half-titanocene”-based catalysts. Secondary (2,1) polyinsertion of p-chlorostyrene into a Ti(III)−alkyl bond has been observed under polymerization conditions. The role of Cp*TiIIIR+ complexes in syndiospecific styrene polymerization has conclusively been confirmed. Furthermore, the reaction of the 13C-enriched complex [Cp*Ti(13CH3)][RB(C6F5)3] with PMe3 and Al(13CH3)3 has also been investigated by ESR spectroscopy. PMe3 displaces the methylborate anion from the coordination sphere of the Cp*Ti13CH3(μ-13CH3)B(C6F5)3 ion pair and produces the corresponding phosphine adduct Cp*Ti(CH3)(PMe3)2+. In the same manner, the reaction of [Cp*Ti(13CH3)][B(C6F5)4] with Al(13CH3)3 affords the [Cp*Ti(μ-13CH3)3Al(13CH3)]+ adduct. The increase of the intensity of the Ti(III) signals observed in the ESR spectra of these catalytic systems after addition of the monomer has been explained on the basis of the ESR results reported above.

Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study

The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl3, itself, incipiently appeared at λmax = 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at λmax = 400 nm arising from delocalization of π-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (“cation-like”), for example, the change of the ionic nature. The intensity decrease at λmax = 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC4H9)4 having a σ-ligand, new and broad UV absorption bands were developed at λmax = 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl3/MAO system. Comparison between the relative absorption intensities at λmax = 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC4H9)4 in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at λmax = 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable β-form seemed to be produced by the CpTiCl3/MAO system independent of the MAO concentration, the Ti(OC4H9)4/MAO system produced a thermally stable α-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of α- and/or β-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1733–1741, 1998

Cationic Titanocene Catalysts for Syndiospecific Polymerization of Styrene

The reaction of pentamethylcyclopentadienyltris((trimethylsilyl)methyl)titanium (Cp*Ti(CH2SiMe3)3) with 1 equiv of B(C6F5)3 was almost quantitative to give the “cationic” compound [Cp*Ti(CH2SiMe3)2...

Fluorinated Half-Sandwich Complexes as Catalysts in Syndiospecific Styrene Polymerization

Fluorinated half-sandwich complexes of titanium, such as CpTiF3, show an increase in activity of up to a factor of 50 compared to chlorinated compounds. In a temperature range of 10−70 °C the excess of methylaluminoxane (MAO) can be reduced to an Al:Ti ratio of 300. The highest melting point of 277 °C can be obtained using pentamethylcyclopentadienyltitanium trifluoride Cp*TiF3. This fluorinated complex affords polymers with a significantly higher molecular weight than with the chlorinated compound. Alkyl substitution of the cyclopentadienyl ligand can increase the activity.

ESR study on SiO2‐supported half‐titanocene catalyst for syndiospecific polymerization of styrene

AbstractMonocyclopentadienyltitanium trichloride (CpTiCl3) was directly immobilized on silica surface. The resulting CpTiCl3/SiO2‐MAO was investigated in view of its suitability for syndiospecific polymerization of styrene using ESR spectroscopy. Polymerization results show that both the syndiotacticity and the activity decrease upon immobilization. A possible explanation is that the active sites may become aspecific after immobilization and part of the immobilized active sites can be leached into the solution in the presence of MAO.

Syndiospecific Styrene Polymerization Promoted by Half-Titanocene Catalysts: A Kinetic Investigation Providing a Closer Insight to the Active Species

Syndiospecific styrene polymerization promoted by mixtures of Cp*TiR3 (R = CH3, CH2Ph) with MAO, B(C6F5)3, and CPh3B(C6F5)4 has been investigated by means of conventional kinetic methods. A first-order kinetics of the monomer in the propagation rate has been determined at 25 °C. At polymerization temperatures higher than 50 °C, the β-H migration from the growing polymer chain to the metal of the active species appears to be the main termination reaction. The average molecular weights of the polymer products depend on the type and coordinating behavior of the counterions ([MAOX]-, [MeB(C6F5)3]-, [(PhCH2)B(C6F5)3]-). The trityl-activated catalysts produce sPS samples with the highest molecular weights. The comparison of the molar concentrations of the active species, determined by kinetic methods, with those of Cp*TiIIIR+ (R = CH3, CH2Ph) evaluated in the polymerization conditions by ESR measurements, confirms the involvement of these complexes in syndiospecific styrene polymerization.

Novel catalysts for syndiospecific polymerization of styrene

The current development of the metallocene-based catalysts for syndiotactic polystyrene (SPS) has been reviewed. SPS is a new semi-crystalline engineering thermoplastic with a crystalline melting point of 270°C. Because of its crystalline nature, SPS has high heat resistance, excellent chemical resistance and waterysteam resistance. In this review, some mechanistic models for polymerization and stereoregulation, as well as the factors which affect the activity and stereospecificity of the catalysts, are discussed.

1-(2-Phenylethyl)-2,3,4,5-tetramethylcyclopentadienyl]- titanium Compounds. Synthesis and Their Use for the Syndiospecific Polymerization of Styrene

A series of monocyclopentadienyltitanium complexes containing the 1-(2-phenylethyl)-2,3,4,5-tetramethylcyclopentadienyl ligand (C5Me4CH2CH2Ph) have been synthesized and characterized. The reaction of C5Me4(SiMe3)CH2CH2Ph (2) with TiCl4 was used to synthesized the trichloro complex (C5Me4CH2CH2Ph)TiCl3 (3), the molecular structure of which was confirmed by an X-ray diffraction study. Compound 3 was further converted into (C5Me4CH2CH2Ph)TiMe3 (4). Reaction of the latter with 1 equiv of [Ph3C][B(C6F5)4] was almost quantitative to give the “cationic” compound [(C5Me4CH2CH2Ph)TiMe2]+[B(C6F5)4]- (5). Complex 5 was thermally unstable in solution and very moisture sensitive. Compound 4 was readily hydrolyzed to [(C5Me4CH2CH2Ph)TiMe2]2(μ-O) (6) upon recrystallization in wet pentane. Structural data indicate intramolecular coordination of the phenyl group to titanium in compound 5, whereas there are no such indications for 3, 4, or 6. The catalytic performance for styrene polymerization of 3 activated with methylal...

Highly Stable Catalysts for the Stereospecific Polymerization of Styrene

The synthesis of eight new catalyst precursors is described, and their catalysis of syndiospecific styrene polymerization when activated by methylaluminoxane (MAO) is compared with IndTiCl3. Phenyl substitution increases polymerization activity (A) in the order 1,3-Ph2Ind < 2-PhInd < 1-PhInd; the opposite trend was observed for the yield (SY) of syndiotactic polystyrene (s-PS). The optimum polymerization temperature (Tp) is 50 °C; an increase of Tp decreases A, SY, and molecular weight (MW) of s-PS. Benz[e]IndTiCl3 (6a) as well as the 2-methyl (6b) and 1,2,3-trimethyl (11) derivatives have been synthesized. Complexes 6a/MAO and 6b/MAO have exceedingly high values of A ≈ 1.8 × 108 g of PS/(mol of Ti·mol of styrene·h) for a turnover rate of 450 s-1, SY over 92%, and MW ≈ 5 × 105. These parameters were only slightly lowered at Tp = 100 °C, indicating very thermally stable, catalytically active species. These catalyst precursors are stable in solution toward air and moisture up to 48 h and are indefinitely stable in the solid state. Though 11/MAO has a lower A, it has a higher SY which changes to lesser degrees with increase in Tp than for either 6a or 6b/MAO. Attempts to make benz[f]indenyltrichlorotitanium have so far been unsuccessful.

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

Mixtures of Cp*TiR3 (with Cp* = C5(CH3)5 and R = CH3, 13CH3) and equimolar amounts of B(C6F5)3 or C(C6H5)3B(C6F5)4, active in the syndiospecific polymerization of styrene, have been investigated by means of ESR spectroscopy. At room temperature the formation of Cp*TiR+ complexes has been observed. Rapid insertion of styrene occurs in Ti−R bonds of these cationic Ti(III) complexes, strongly suggesting their role in the stereospecific polyinsertion.

Mao based catalysts for syndiotactic polystyrene (sPS)

AbstractSeveral non‐metallocene (Ti, Zr) and substituted mono‐Cp titanium metallocenes have been tested in the presence of methylalumoxane (MAO) as catalyst for syndiospecific polymerization of styrene. Effect of substitutions on the titanium and Cp ligand, molar ratio of Al/Ti, TMA and temperature on activity, Mwt. and % sPS were studied. CpTi(OiPr)3 gives a less active catalyst than Cp*Ti(OiPr)3 and the resulting sPS is less stereoregular and of lower molecular weight.

Syndiospecific polymerization of styrene with arene titanium(II) complexes as catalyst precursors

AbstractThe divalent titanium compounds [(η6‐C6H5Me)Ti(Cl2AlCl2)2] (1) and [(η6‐C6Me6)Ti(Cl2AlCl2)2] (2) are syndiospecific catalysts in the polymerization of styrene when activated with methylaluminoxane. The polystyrene is of exceptionally high molecular weight.

A combined NMR and electron spin resonance investigation of the (C5(CH3)5)Ti(CH2C6H5)3/B(C6F5)3 catalytic system active in the syndiospecific styrene polymerization

AbstractThe reaction of (C5(CH3)5)Ti(CH2C6H5)3 with B(C6F5)3 in chlorobenzene at 25°C produces a mixture of [(C5(CH3)5)Ti(CH2C6H5)2]+ [B(CH2C6H5)(C6F5)3]− (1) and Ti(III) complexes which have been characterized by NMR and electron spin resonance (ESR) spectroscopy, respectively. Spectroscopic data combined with polymerisation activity measurements suggest that a Ti(III) complex is the active species in the styrene syndiospecific polymerisation.