NMR analysis of Ti(NEt2)4–AlMe3 catalyst system and its polymerization activity

Studies have been made by NMR and ESR spectroscopy to elucidate the reaction mechanism in which the Ti(NEt₂)₄–AlMe₃ catalyst system is involved. The two reaction products of Ti(NEt₂)₃Me and Al(NEt₂)Me₂ have been confirmed by NMR spectroscopy when Ti(NEt₂)₄ is reacted with AlMe₃, and two kinds of paramagnetic species have been noted by ESR spectroscopy. It has been found that Ti(NEt₂)₃Me plays an important role as an active species for the polymerization of styrene.     

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp₂ZrCl₂ and rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂ as a catalyst) and styrene (Cp*Ti(OMe)₃ as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp₂ZrCl₂/MAO, whereas it became less effective when the catalyst changed to rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp₂ZrCl₂/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂/MAO. In the case of styrene polymerization with Cp*Ti(OMe)₃/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010     

Nd(OR)3-mClm-AlEt3 catalyst system in the polymerization of butadiene: I. The general feature of polymerization

Homopolymerization of butadiene has been carried out with a new series of binary catalyst system Nd(OR)_3-mG_m-AlEt₃. The catalytic activity as well as the microstructure of the resulting polymer have been studied. The results indicate that the stereospecificity of the polybutadiene obtained with these binary catalyst system (when m = 2) is similar to that prepared with ternary system Nd(OR)₃-Al₂Et₃Cl₃-AlEt₃, yet the catalytic activity of the former is somewhat higher. Thus possibly, the present simpler binary system is preferable to the ternary system when applied to the polymerization of butadiene.     

Monomer-Isomerization polymerization. XXVIII. Catalytic activity of transition metals and alkylaluminums in monomer-isomerization polymerization of 2-butene

Monomer-isomerization polymerization of cis-2-butene (c2B) with Ziegler–Natta catalysts was studied to find a highly active catalyst. Among the transition metals [TiCl₃, TiCl₄, VCl₃, VOCl₃, and V (acac)₃] and alkylauminums used, TiCl₃? R₃Al (R = C₂H₅ and i-C₄H₉) was found to show a high-activity for monomer-isomerization polymerization of c2B. The polymer yield was low with TiCl₄? (C₂H₅)₃Al catalyst. However, when NiCl₂ was added to this catalyst, the polymer yield increased. With TiCl₃? (C₂H₅)₃Al catalyst, the effect of the Al/Ti molar ratio was observed and a maximum for the polymer yields was obtained at molar ratios of 2.0–3.0, but the isomerization increased as a function of Al/Ti molar ratio. The valence state of titanium on active sites for isomerization and polymerization is discussed.     

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     

Simultaneous polymerization and formation of polyacetylene film on the surface of concentrated soluble Ziegler-type catalyst solution

A direct method of simultaneously polymerizing and forming acetylene monomer to produce uniformly thin films of polyacetylene was investigated in terms of catalyst system, catalyst concentration, and polymerization temperature. The best catalyst was a Ti(OC₄H₉)₄,–AI(C₂H₅)₃ system (Al/Ti = 3–4) and the critical concentration was 3 mmole/l. of Ti(OC₄H₉)₄. Below the critical concentration, only a solid or a powder was obtained. The configuration of the polymers obtained depends strongly upon the polymerization temperature. Thus an all-cis polymer was obtained at temperatures lower than −78°C, whereas an all-trans polymer resulted at temperatures higher than 150°C. Observations either in an electron microscope by direct transmission or in a scanning electron microscope showed that the film is composed of an accumulation of fibrils about 200–300 Å in width and of indefinite length.     

High-Resolution Proton Magnetic Resonance Analysis of Polypropylenes

The dyad and triad tacticities of polypropylenes were determined quantitatively with the aid of a computer form the 100-MHz proton magnetic resonance spectra in o-dichlorobenzene solution at 165[ddot]C. The contents of tactic dyad and traid evaluated from the 100-MHz PMR spectra are in fair agreement with the values determined from the 220-MHz PMR and ¹³C-(¹H) spectra, respectively. The fraction soluble in boiling ethyl ether of polymer prepared with the Ti(O-n-Bu)Cl₃-AlEt₂ Cl catalyst shows a character of stereorandomness, and the ethyl ether-soluble portion of polymer polymerized with the TiCl₃-AlEt₂ Cl catalyst has a character of stereoblock sequence. Furthermore, by IR analysis, it has become apparent that the former has a (CH₂)₂ group formed by two propylene units in a tail-to-tail arrangement.     

Syndiospecific polymerization of styrene using a heterogeneous titanocene catalyst

A supported-catalyst system for the polymerization of styrene was prepared by the immobilization of pre-activated indenyl titanium trichloride (IndTiCl₃) with methylaluminoxane (MAO) on silica. This catalyst showed a higher productivity using a smaller amount of metallocene on the catalyst support. Other polymerization conditions that affect the productivity of the catalyst, including the ratio of Ti/SiO₂ (wt%) and Al/Ti, and the time for polymerization, were also investigated. The polymers obtained from this system were extracted using methylethyl ketone and the syndiotacticity was calculated from the weight of the remaining insoluble polymer. With these optimized conditions, and the use of a heterogeneous catalyst, we developed a more efficient catalyst system that is more suitable for industrial applications than previously developed systems.     

Polymerization of 4-phenyl-1-butyne catalyzed by metathesis and Ziegler–Natta catalysts

The polymerization of 4-phenyl-1-butyne was carried out using metathesis and Ziegler-Natta catalysts. Especially, the Fe(acac)₃-AlEt₃ catalyst with toluene as a solvent produced an extremely high molecular weight polymer of M_w ≈ 10⁶. Solubility of the polymers at room temperature in organic solvents such as benzene, toluene, dichloromethane, chloroform, and THF was excellent despite their high molecular weights. It has been indicated that the polymer prepared by the Fe(acac)₃-AlEt₃ catalyst is of cis form with a high stereoregularity. © 1993 John Wiley & Sons, Inc.     

Growth of polystyrene films via gas‐phase polymerization with [Pd(CH3CN)4][BF4]2 thin film catalyst

The heterogeneous catalytic polymerization of styrene vapor with a tetrakis(acetonitrile)palladium(II) tetrafluoroborate, [Pd(CH₃CN)₄][BF₄]₂, thin film has been demonstrated. The catalyst is deposited by nebulization of dilute solutions onto a quartz crystal microbalance (QCM) and then exposed to styrene vapor in controlled environments. The use of QCM allows in situ monitoring of catalyst deposition and polymer growth kinetics. The polymerization process appears to involve the entire catalyst film rather than polymerization only at the catalyst film surface. The styrene vapor polymerization occurs rapidly after a short induction time needed for monomer dissolution and catalyst activation. The narrow molecular weight distribution of the produced polymer suggests that the deposited film acts as a single site catalyst. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1930–1934, 2005     

Simultaneous polymerization and formation of polyacetylene film on the surface of concentrated soluble Ziegler-type catalyst solution

A direct method of simultaneously polymerizing and forming acetylene monomer to produce uniformly thin films of polyacetylene was investigated in terms of catalyst system, catalyst concentration, and polymerization temperature. The best catalyst was a Ti(OC₄H₉)₄–Al(C₂H₅)₃ system (Al/Ti = 3–4) and the critical concentration was 3 mmole/l. of Ti(OC₄H₉)₄. Below the critical concentration, only a solid or a powder was obtained. The configuration of the polymers obtained depends strongly upon the polymerization temperature. Thus an all-cis polymer was obtained at temperatures lower than ?78°C, whereas an all-trans polymer resulted at temperatures higher than 150°C. Observations either in an electron microscope by direct transmission or in a scanning electron microscope showed that the film is composed of an accumulation of fibrils about 200–300 Å in width and of indefinite length.     

Polymerization of vinyl chloride by the Ti(O-n-Bu)4–AlEt3–epichlorohydrin catalyst system

The polymerization of vinyl chloride was carried out by using a catalyst system consisting of Ti(O-n-Bu)₄, AlEt₃, and epichlorohydrin. The polymerization rate and the reduced viscosity of polymer were influenced by the polymerization temperature, AlEt₃/Ti(O-n-Bu)₄ molar ratios, and epichlorohydrin/Ti(O-n-Bu)₄ molar ratios. The reduced viscosity of polymer obtained in the virtual absence of n-heptane as solvent was two to three times as high as that of polymer obtained in the presence of n-heptane. The crystallinity of poly(vinyl chloride) thus obtained was similar to that of poly(vinyl chloride) produced by a radical catalyst. It was concluded that the polymerization of vinyl chloride by the present catalyst system obeys a radical mechanism rather than a coordinated anionic mechanism.     

Preparation of Titania from Tetrakis(diethylamino)titanium via Hydrolysis

The conversion of tetrakis(diethylamino)titanium (Ti(NEt₂)₄) into titania via either a combination of hydrolysis (Ti(NEt₂)₄ : THF : H₂O = 1 : 10 : x, x = 2, 4, 10) at ambient conditions and calcination (method A) or hydrolysis in a water-tetrahydrofuran (THF) mixture (Ti(NEt₂)₄ : THF : H₂O = 1 : 10 : 100) at reflux (method B) was investigated. Titanium tertiary butoxide (Ti(O ^t Bu)₄) was also used as a substitute for Ti(NEt₂)₄. The hydrolysis via method A resulted in the formation of amorphous solids containing organics. Thermal analyses showed that the hydrolysis products showed mass losses up to 500°C probably due to the presence of diethylamine (Et₂NH) formed via the hydrolysis of Ti(NEt₂)₄ in the hydrolysis products, while a mass loss of the hydrolysis product from Ti(O ^t Bu)₄ was completed up to about 200°C. After calcination at 600°C, anatase or a mixture of anatase and rutile was obtained. The crystallization behavior of the hydrolysis products from Ti(NEt₂)₄ was different from that of the hydrolysis product from Ti(O ^t Bu)₄. The hydrolysis via method B gave only an amorphous material from Ti(NEt₂)₄, while a crystalline titania (anatase and brookite) formed from Ti(O ^t Bu)₄.     

(η5-Pentamethylcyclopentadienyl)trimethyltitanium as a precursor for the syndiospecific polymerization of styrene

An equimolar mixture of Cp*Ti(CH₃)₃ (2) and Ph₃C⁺[B(C₆F₅)₄]^? (1) forms a highly active and syndioselective catalyst for the polymerization of styrene, producing 96% syndiotactic polystyrene (PS) at an activity of 0.91 × 10⁷ g PS (mol Ti)^?1 (mol styrene)^?1 h^?1. Both activity and syndioselectivity can be increased using tri–isobutylaluminum (TIBA) to scavenge the system. ESR measurements indicate that the polymerization proceeds via titanium(IV) intermediates. Catalysts derived from 2/methylaluminoxane (MAO) as well as Cp*TiCl₃/MAO also function as syndioselective styrene polymerization catalysts, but are less active than the ‘cationic’; system derived from 1 and 2.     

Polymerization of vinyl chloride with half‐titanocene/methylaluminoxane catalysts

The polymerization of vinyl chloride (VC) with half‐titanocene /methylaluminoxane (MAO) catalysts is investigated. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst (Cp* = η⁵‐pentamethylcyclopentadienyl) afforded high‐molecular‐weight poly(vinyl chloride) (PVC) in good yields, although the polymerization proceeded at a slow rate. With the Cp*TiCl₃/MAO catalyst, the polymer was also obtained, but the polymer yield was lower than that with the Cp*Ti(OCH₃)₃/MAO catalyst. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was influenced by the MAO/Ti mole ratio and reaction temperature, and the optimum was observed at the MAO/Ti mole ratio of about 10. The optimum reaction temperature of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was around 20 °C. The stereoregularity of PVC obtained with the Cp*Ti(OCH₃)₃/MAO catalyst was different from that obtained with azobisisobutyronitrile, but highly stereoregular PVC could not be synthesized. From the elemental analyses, the ¹H and ¹³C NMR spectra of the polymers, and the analysis of the reduction product from PVC to polyethylene, the polymer obtained with Cp*Ti(OCH₃)₃/MAO catalyst consisted of only regular head‐to‐tail units without any anomalous structure, whereas the Cp*TiCl₃/MAO catalyst gave the PVC‐bearing anomalous units. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst did not inhibit even in the presence of radical inhibitors such as 2,2,6,6,‐tetrametylpiperidine‐1‐oxyl, indicating that the polymerization of VC did not proceed via a radical mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 248–256, 2003     

The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl‐amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl‐amide titanium catalyst systems [η⁵,η¹‐C₅H₄(CH₂)₂NR]TiCl₂/MAO and [η⁵,η¹‐C₅H₄(CH₂)₂NR]Ti(CH₂Ph)₂/B(C₆F₅)₃ (R = ^tBu, ⁱPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl‐amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation‐anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth.     

Reactivity of tetrathiometalates with alkynes. Synthesis and characterisation of dithiolene complexes of Mo,W, and V by ESMS and XRD

The reaction of DMA (C₂(CO₂Me)₂) with MoS₄²⁻, WS₄²⁻, and VS₄³⁻ led to six dithiolene compounds. (NEt₄)₂[Mo₂(X)₂(μ-S) ₂(η²-S₂C₂(CO₂Me)₂)₂] 1, (X = O or S), (NEt₄)₂[V(η²-S₂C₂(CO₂Me)₂)₃] 2a, (NEt₄)₂[V(O)(η²-S₂C₂(CO₂Me)₂)₂] 2b, (NEt₄)₂[W₂(S)₂(μ-S)₂(η²-S₂C₂(CO₂Me)₂)₂] 3, (NEt₄)₂[W(O)(η²-S₂C₂(CO₂Me)₂)₂] 4 and (NEt₄)₂[W₂(μ-S)₂(η² -S₂C₂(CO₂Me)₂)₄] 5 were isolated in the solid state. The structures of 2a, 3, 4 and 5 were determined by single crystal X-ray diffraction study. The compounds 1 and 2b were characterised in solution by ESMS (Electrospray Mass Spectrometry) and in the solid state by IR spectroscopy. ESMS data also allowed proposal of a reaction scheme which rationalizes the formation of the different species present in solution.     

Titanium complexes bearing carbamato ligands as catalytic precursors for propylene polymerization reactions

This report describes propylene polymerization reactions with titanium complexes bearing carbamato ligands, Ti(O₂CNMe₂)Cl₂ ( I ) and Ti(O₂CR₂)₄ [R₂ = NMe₂ ( II ), NEt₂ ( III ) and ( IV )]. Combinations of these complexes and MAO form catalysts for the synthesis of atactic polypropylene, as confirmed by FT‐IR, DSC and ¹³C NMR analysis. Effects of main reaction parameters on the catalyst activity were studied including the type of complex, solvent, temperature, and the [Al]/[Ti] molar ratio. The highest activity was observed when chlorobenzene was used as a solvent and AlMe₃‐depleted MAO was employed as a cocatalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4095–4102     

Monomer-isomerization polymerization. XXIII.. Monomer-isomerization polymerization of 5-phenyl-2-pentene with ziegler–natta catalysts

5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl₃–R₃Al (R = C₂H₅ or i-C₄H₉, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl₃ was in the following order: (C₂H₅)₃Al > (i-C₄H₉)₃Al > (C₂H₅)₂AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl₃–(C₂H₅)₃Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)₂], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios.     

Various silyl-substituted cyclopentadienyl titanium complexes [CpSi(CH3)2X]TiCl3 as catalysts for syndiotactic polystyrene

Three silyl-substituted titanium trichloride complexes [CpSi(CH₃)₂X]TiCl₃ [X=Cl(1), Me(2), PhOMe(3)] were tested as catalyst precursors for the syndiospecific polymerization of styrene. The catalytic activity increased in the order 1 > 2 > 3. The highest activity was 2.42 × 10⁷ g s-PS/mol Ti mol S h using complex 1/MAO catalytic system at molar ratio of Al/Ti=2000. The effects of variation on polymerization temperature and Al/Ti ratio on the polymerization of styrene were also studied.