Syndiospecific polymerization of styrene catalyzed by CpTiCl2(OR) complexes

Five new CpTiCl₂(OR) alkoxyl-substituted half-sandwich complexes, where R was methoxyethyl ( 1 ), methoxypropyl ( 2 ), methoxyisopropyl ( 3 ), o-methoxyphenyl ( 4 ), or tetrahydrofurfuryl ( 5 ), were synthesized, characterized, and tested as catalyst precursors for the syndiospecific polymerization of styrene. These precursors were more active than (η⁵-cyclopentadienyl)trichlorotitanium (CpTiCl₃). The different structures of the alkoxyl ligands affected the activity slightly. When the polymerization was carried out in bulk, all the complexes ( 1–5 ) exhibited high activities, even at the low molar ratio of Al/Ti = 300. The syndiotactic polystyrene (s-PS) percentage of the polymer produced by alkoxyl-substituted complexes was much higher than that of CpTiCl₃. The really active center might be described as [CpTiMe]⁺ · [MAOX]⁻ · nMAO (where MAO is methylaluminoxane). The normal active species [CpTiMe]⁺ made up the core and the anion mass [MAOX]⁻ · nMAO surrounded the core and constituted the outer shell circumstance. They activated the syndiospecific polymerization of styrene as a whole. For a high concentration of MAO, the function of the alkoxyl group was weak because of the limited proportion in the outer shell. For a low concentration of MAO, the proportion of alkoxyl ligands in the outer shell increased greatly, and their influence also became significant, as reflected in a higher s-PS percentage of the obtained polymer. The existence of the additional oxygen atom in the alkoxyl ligand stabilized the active species more effectively; this was reflected in the higher temperature of the maximum activities. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1817–1824, 2001     

Polymerization of styrene with supported half-sandwich complexes

Polymerizations of styrene were carried out with half-sandwich complexes supported on silica, CpTiX₃/MAO/SiO₂ (X = Cl, F). The optimum values for the polymerization time, the amount of cocatalyst and the Al_support/Ti ratio were found for the trichlorinated system. The highest activity obtained was 3,100 g sPS/(mol Ti × h × mol/L styrene). The trihalogenated complexes were compared to one another with respect to their polymerization rate. CpTiCl₃/MAO/SiO₂ and CpTiF₃/MAO/SiO₂ behave in a similar manner, suggesting that the active species of both half-sandwich complexes on the support are the same. Furthermore, aging experiments were carried out with CpTiCl₃/MAO/SiO₂ and, surprisingly, deactivation was observed, as opposed to supported zirconocenes which gain stability against deactivation reactions when anchored to a carrier. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2959–2968, 1999     

CpTiCl2(OR)/MAO体系催化苯乙烯间规聚合的研究

茂金属催化剂广泛应用于催化α-烯烃和苯乙烯的定向聚合. 与传统的Ziegler-Natta催化剂相比, 茂金属催化剂催化活性中心单一, 聚合过程立体定向性强, 且往往得到用常规方法所不能得到的新型聚合物［1～5］. Ishihara等［6］首次采用钛金属有机化合物与甲基铝氧烷(MAO)体系催化苯乙烯聚合, 分离得到间规聚苯乙烯, 从此揭开了苯乙烯定向聚合的新篇章, 合成了大量茂金属有机化合物, 用于催化苯乙烯间规聚合, 其中半夹心结构的茂金属化合物CpTiX3［7,8］, IndTiCl3［3,4,9,10］［Cp=(未)取代环戊二烯基, Ind=(未)取代茚基; X=Cl, F, 烷氧基等］具有最好的催化活性及间规定向性. (CpHMe4)TiF3［8］催化活性高达1.01×108 g PS/(mol Ti*h), 间规度≥95%.     

ESR study on styrene polymerization with CpTiCl3/MMAO: Effect of monomer addition on catalyst activity

An on-line electron spin resonance (ESR) technique was applied to investigate the syndiospecific polymerization of styrene activated by the catalyst system CpTiCl₃/MMAO. The measurements included trivalent titanocene concentration and monomer conversion. The activation procedure was found to have a dramatic effect on catalyst activity. Adding the reactants in the order of (MMAO + CpTiCl₃) + St gave a much higher trivalent titanocene concentration and catalyst activity than the order of (MMAO + St) + CpTiCl₃. The catalyst deactivation behaviors in the temperature range of 25–70°C were followed as a function of time during polymerization. At high Al/Ti ratios (500–1000), the decay rates of trivalent titanocene in the presence of styrene were much faster than those of the pure catalyst system. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3385–3390, 1999     

Copolymerization of ethene with styrene using different methylalumoxane activated half-sandwich complexes

Ethene was copolymerized with styrene using five different methylalumoxane (MAO) activated half-sandwich complexes of the general formula Me₂Si(Cp)(N R)MCl₂, varying the substituents on the cyclopentadienyl ring and the substituent on the amide (Cp = tetramethylcyclopentadiene CBT , 1-indenyl IBT , 3-trimethylsilyl-1-indenyl SIBT , or fluorenyl FBZ , R = tert-butyl (complexes CBT, IBT, SIBT, FBZ ) or benzyl CAT ), as well as the metal center (M = Ti, except FBZ : M = Zr). Polymerization behavior was analyzed with respect to catalyst activity and polymerization kinetics, styrene incorporation, copolymer microstructure, and molecular weight. All complexes produced random poly(ethene-co-styrene) without any regioregular or stereoregular microstructure. Complex CBT showed the highest catalytic activity, the fluorenyl-substituted complex FBZ produced the highest molecular weight polymer, and complexes SIBT and CAT promoted high styrene incorporation. Cp-substitution pattern influenced deactivation of the catalytic system with bulky substituents of the Cp-ring slowing down deactivation at the expense of styrene incorporation. Moreover, deactivation was accelerated with increasing styrene concentration. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1571–1578, 1997     

The syndiospecific polymerization of styrene in the presence of fluorine‐containing half‐sandwich metallocenes

The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η⁵‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η⁵‐octahydrofluorenyl titanium tristrifluoro‐acetate, η⁵‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η⁵‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)₃ > [Cp*Ti(OCOCF₃)₂]₂O ≈ Cp*TiCl₃, and for octahydrofluorenyl compounds, [656]Ti(OMe)₃ > [656]Ti(OCOC₆F₅)₃ > [656]Ti(OCH₃)₂(OCOCF₃) > [656]Ti (OCOCF₃)₃. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000     

Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands-MAO catalyst systems

Various half-sandwich titanium complexes containing iminoimidazolidide ligands, CpTiCl(2)[1,3-R(2)(CH(2)N)(2)C=N] (1a-d) [R = Ph (a), 2,6-Me(2)C(6)H(3) (b), cyclohexyl (c), (t)Bu (d)], have been employed as the catalyst precursors for ethylene polymerisation, syndiospecific styrene polymerisation, and copolymerisation of ethylene with 1-hexene in the presence of MAO cocatalyst; 1d showed the highest catalytic activity for ethylene polymerisation whereas 1b showed the highest activity for syndiospecific styrene polymerisation.     

Syndiospecific Polymerization Catalysts for Styrene Based on Rare Earth Metal Half-Sandwich Complexes

In the presence of an trialkyl aluminum cocatalyst the activation of scandium, yttrium and lutetium mono(cyclopentadienyl) complexes with various substituted cyclopentadienyl ligands by [Ph₃C][B(C₆F₅)₄] results in highly efficient catalysts for the syndiospecific polymerization of styrene. As active species half-sandwich alkyl cations is assumed that is isostructural with the mono(cyclopentadienyl) titanium alkyl cation originally proposed by Zambelli.     

Ethylene polymerization reactions with Ziegler–Natta catalysts. III. Chain-end structures and polymerization mechanism

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions¹ provided the basis for a new kinetic scheme that postulates the equilibrium formation of Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the Ti H bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4281–4294, 1999     

Olefin polymerization by cyclopentadienyltris(dimethylamido)titanium(IV) complexes

Several titanium(IV) complexes of the type Cp′Ti(NMe₂)₃ [Cp′ = cyclopentadienyl ( 1 ), (dimethylaminoethyl)cyclopentadienyl ( 2 ), indenyl ( 3 ), and pentamethylcyclopentadienyl ( 4 )] were prepared, and their catalytic properties in the polymerization of α‐olefins were examined. Complexes 1 and 2 catalyzed the polymerization of ethylene in the presence of methylaluminoxane with a much higher activity than 3 or 4 . Complexes 3 and 4 polymerized ethylene with an activity similar to that of CpTiCl₃ ( 6 ). The preactivation of 2 , 3 , or 4 with trimethylaluminum (TMA) resulted in an increase in ethylene polymerization activities. Also, 1 and 2 were successfully used as ethylene/1‐hexene copolymerization catalysts, producing polymers with various amounts of 1‐hexene incorporation, depending on the amount of 1‐hexene in the feed mixture. Complex 1 likewise effectively polymerized styrene with a higher activity and higher syndiospecificity than the other three catalysts. Complexes 3 and 4 polymerized styrene with low syndiospecificity, whereas 2 produced only atactic polystyrene. The preactivation of 3 or 4 with TMA resulted in an increase in styrene polymerization activities and increased the syndiotacticity percentage of the polymers produced. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 313–319, 2001     

Olefin polymerization with Me4Cp–Amido complexes with electron‐withdrawing groups

A series of Me₄Cp–amido complexes {[η⁵:η¹‐(Me₄C₅)SiMe₂NR]TiCl₂; R = t‐Bu, 1 ; C₆H₅, 2 ; C₆F₅, 3 ; SO₂Ph, 4 ; or SO₂Me, 5 } were prepared and investigated for olefin polymerization in the presence of methylaluminoxane (MAO). X‐ray crystallography of complexes 3 and 4 revealed very long Ti N bonds relative to the bonds of 1 . These complexes were employed for ethylene–styrene copolymerizations, styrene homopolymerizations, and propylene homopolymerizations in the presence of MAO. The productivities of the catalysts derived from 3 – 5 were much lower than the productivity of the catalyst derived from 1 for the propylene polymerizations and ethylene–styrene copolymerizations, whereas the styrene polymerization activities were much higher for the catalysts derived from 3 – 5 than for the catalyst derived from 1 . The polymerization behavior of the catalysts derived from the metallocenes 3 – 5 were more reminiscent of monocyclopentadienyl titanocene Cp′TiX₃/MAO catalysts than of CpATiX₂/MAO catalysts such as 1 containing alkylamido ligands. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4649–4660, 2000     

Syndiospecific polymerization of styrene with BzCpTiCl3 and methylaluminoxane as cocatalysts

Benzyl cyclopentadienyl titanium trichloride (BzCpTiCl₃) was synthesized from benzyl bromide, cyclopentadienyl lithium, and titanium tetrachloride and used in combination with methylaluminoxane (MAO) for the syndiospecific polymerization of styrene. Kinetic measurements of the polymerization were carried out at different temperatures. The polymerization with BzCpTiCl₃/MAO differs from the polymerization with cyclopentadienyl titanium trichloride in its behavior toward the Al/Ti ratio. In addition, high activities are observed at high Al/Ti ratios. By analyzing the polymerization runs and the physical properties of the polymers with differential scanning calorimetry, ¹³C NMR spectroscopy, wide‐angle X‐ray scattering measurements, and gel permeation chromatography, we found that the phenyl ring coordinates to the titanium atom during polymerization. Other known substitutions of the cyclopentadienyl ring (V. Scholz, Dissertation, University of Hamburg, 1998) in principle influence the polymerization activity. The physical properties of the polymers produced by the catalysts already known are nearly identical. BzCpTiCl₃ is the first catalyst that leads to polystyrene obviously different from the polystyrene produced by other highly active catalysts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2805–2812, 2001     

Studies of ethylene–styrene copolymerization with dinuclear constrained geometry complexes with methyl substitution at the five‐membered ring in indenyl of [Ti(η5:η1‐C9H5SiMe2NCMe3)]2 [CH2]n

The new dinuclear half‐sandwich CGC (constrained geometry catalyst) with methyl substitution in indenyl, [Ti(η⁵:η¹‐2‐methylindenyl)SiMe₂NCMe₃]₂ [(CH₂)_n] [n = 6 ( 10 ), n = 9 ( 11 ), n = 12 ( 12 )], have been synthesized, and structure of these complexes has been characterized by ¹H and ¹³C NMR. The most important feature is that two protons of methylene directly bonded to the indenyl ring become inequivalent to be shown as two separated resonances at 2.9 and 3.0 ppm, probably due to the formation of planar chirality caused by a titanium complex formation. It has been found that the dinuclear CGCs with methyl substitution at an indenyl ring were very active catalysts for ethylene and styrene copolymerization. The activity increases in the order of 10 < 11 < 12 , which indicates that the presence of a longer bridge between two active sites contributes to facilitate the polymerization activity of the dinuclear CGC more effectively. This result might be understood by the implication that the steric factor rather than the electronic factor may play a major role to direct the polymerization behavior of the dinuclear CGC. It is found that the dinuclear catalysts are very efficient to incorporate styrene in the polyethylene backbone. The styrene contents in the formed copolymers ranged from 5 to 40% according to the polymerization conditions. One can observe strong signals at 29.7 ppm of the polyethylene sequences, and, in addition, peaks at 27.5, 36.9, and 46. 2ppm (S_βδ, S_αδ, and T_δδ, respectively) of sequences of EESEE. Weak peak at 25.3 ppm are attributed to S_ββ, which represents SES sequence. The absence of a signal for T_ββ at 41.3 ppm and for S_αα at 43.6 ppm shows there is no styrene–styrene sequences in copolymers. This result indicates that the dinuclear CGC are very effective to generate well‐distributed poly(ethylene‐co‐styrene)s. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1712–1723, 2004     

Steric and electronic effects of the R in IndTiCl2(OR) catalysts on the syndiospecific polymerization of styrene

Four alkoxyl ligand substituted indenyl titanium dichloride complexes, IndTiCl₂(OR) (R=Me (2), Et (3), ⁱPr (4), cyclohexyl (5)) were prepared, and evaluated as catalysts for the syndiospecific polymerization of styrene when activated with methylaluminoxane (MAO). Alkoxyl ligand substituted complexes showed higher catalytic activities than IndTiCl₃ (1) except for complex 5. When R=Et, the catalyst 3 showed the highest activity. A study of the steric and electronic effects of alkoxyl ligand revealed that the more electron-donating and less steric bulky R group was more suitable for the improvement of the catalytic activity. When the polymerization was carried in solution at high molar ratio of Al/Ti=4000, the s-PS% of obtained polymer were in the range of 99.0–99.6%. The highest melting point of 276.9°C was obtained by using 2 as catalyst. The influence of polymerization temperature was also investigated. The maximum polymerization activities were found at 50°C for all of the above complexes, but the percentages of s-PS were insensitive to the polymerization temperature.     

Syndiospecific polymerization of styrene with Cp*TiCl((OCH(R)CH2)2NAr)/MMAO

A series of titanium complexes Cp*TiCl((OCH(R)CH₂)₂NAr) (Cp* = C₅Me₅, R = H, Ar = Phenyl ( 2a) ; R = H, Ar = 2,6‐dimethylphenyl ( 2b ); R = Me, Ar = Phenyl ( 2c )) was prepared by the reaction of corresponding N,N‐diethoxylaniline derivatives, with Cp*TiCl₃ in the presence of excessive triethylamine. All the titanium complexes display higher catalytic activities towards the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as a cocatalyst, and produce higher molecular weight polystyrenes with higher syndiotacticity and melting temperature than their mother complex Cp*TiCl₃. The catalyst activities and polymer yields as well as polymer properties are considerably affected by the steric and electronic effect of the tridentate ligands. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1562–1568, 2005     

单茂钛催化剂的苯乙烯间规聚合和乙烯聚合的比较

考察三甲基铝（ＴＭＡ） 部分水解法制备固体改性甲基铝氧烷（ｍ ＭＡＯ） 时,反应物Ｈ２Ｏ 和ＴＭＡ 的摩尔比对ｍ ＭＡＯ 的产量及ｍ ＭＡＯ 中ＴＭＡ 含量的影响;以五甲基茂基三苄氧基钛［Ｃｐ ＊ Ｔｉ（ＯＢｚ）３］／ｍ ＭＡＯ 组成的均相催化体系,分别考察ｍ ＭＡＯ 的用量［ 即Ａｌ／Ｔｉ 摩尔比］ 及ｍ ＭＡＯ 中ＴＭＡ 含量对苯乙烯间规聚合和乙烯聚合的影响．通过分析Ｃｐ ＊ Ｔｉ（ＯＢｚ）３／ｍ ＭＡＯ 催化体系钛氧化态的分布,发现Ｔｉ（ Ⅲ） 活性中心有利于合成间规聚苯乙烯;而Ｔｉ（ Ⅳ） 活性中心有利于合成聚乙烯．苯乙烯间规聚合时,外加三异丁基铝（ＴＩＢＡ） ,将提高催化活性,同时可节省ＭＡＯ 用量．     

Preparation of micron-size polystyrene particles in supercritical carbon dioxide

The dispersion polymerization of styrene in supercritical CO₂ utilizing poly(1,1-dihydroperfluorooctyl acrylate) (p-FOA) as a polymeric stabilizer was investigated as well as poly(1,1-dihydroperfluorooctyl methacrylate) (p-FOMA). The resulting high yield (>85%) of spherical and relatively uniform polystyrene (PS) particles with micron-size range (2.9–9.6 µm) was formed for 40 h at 370 bar using various amounts of p-FOA and p-FOMA as a stabilizer with good stability until the end of the reaction. The particle diameter was shown to be dependent on the weight percent of added stabilizer. Previously, we reported that p-FOA was not effective for the dispersion polymerization of styrene as a stabilizer. Here, we find that p-FOA can indeed be an effective stabilizer for the dispersion polymerization of styrene in supercritical CO₂, but the pressure necessary to achieve good stability is higher than pressure used by us previously. This study suggests the possibility that fluorinated acrylic homopolymers are effective for the dispersion polymerization of various kinds of monomers as a stabilizer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2429–2437, 1999     

Ethylene polymerization reactions with Ziegler–Natta catalysts. II. Ethylene polymerization reactions in the presence of deuterium

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C₂H₅ groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D₂ is used as a chain transfer agent instead of H₂, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D₂. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp₂ZrCl₂ MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH₂ CH₂ (CH₂ CH₂)_x CH₂ CH₂D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999     

Coordination polymerization at very low amounts of methylaluminoxane as cocatalyst

The effect of very low amounts of methylaluminoxane as an activating cocatalyst in the coordination polymerization has been investigated in the syndiospecific polymerization of styrene with a half-sandwich metallocene catalyst in the presence of triisobutylaluminum at molar ratios of methylaluminoxane/transition metal from 0/1 to about 20/1 in comparison to the polymerization behavior at high molar methylaluminoxane (MAO)/metal ratios.As a result, there cannot be observed any polymerization reaction below a true molar ratio MAO/Ti of 6:1. At higher molar ratios until about 20, the polymerization conversion is increasing significantly with the MAO/Ti molar ratio.These observations and the results of the determination of the kinetic reaction order can be explained with Barron’s tert-butyl aluminoxane based model of MAO as a cage of six monomeric MAO units (AlOMe)₆ in contrast to Sinn’s MAO model of a cage of twelve monomeric units (AlOMe)₁₂ and are discussed with the results received at usually applied much higher MAO/transition metal ratios leading to a first-order dependence of the polymerization rate on the MAO concentration.From the thermal behavior of the syndiotactic polystyrenes synthesized it can be concluded, that the stereospecificity of the polymerization reaction is not affected by MAO at low MAO concentrations.     

Novel catalyst compositions for the syndiospecific polymerization of styrene prepared by the combination of cyclopentadenyl complexes of group IIA or group IIIA elements with titanium alkoxides

A highly reactive catalyst system, which induces the syndiospecific polymerization of styrene with high activity, has been found by the combination of cyclopentadienyl (Cp) complexes of group IIA or group IIIA elements with titanium alkoxides. The ¹H NMR monitoring of these reactions reveals the occurrence of a novel Cp‐transfer reaction that leads to the generation of Cp‐containing titanium complexes as catalysts for promoting the syndiospecific polymerization of styrene. Detailed in situ ¹H NMR studies reveal that the rate of the Cp‐transfer reaction is highly dependent on the steric bulkiness of the titanium alkoxide complexes, the structures of the Cp complexes of group IIA or group IIIA elements, and the polymerization temperature. Styrene polymerization studies also reveal that a more effective Cp‐transfer reaction can typically lead to the generation of a more highly reactive catalyst for sPS polymerization. This study provides a convenient method for the in situ generation of variable structures of Cp/titanium alkoxide complexes, which are difficult to synthesize by other methods. Most importantly, the mixture of a catalyst precursor can be directly used as an sPS polymerization catalyst without isolation and purification of Cp/titanium complexes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2304–2315, 2005