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

The effects of residual trimethylaluminum (TMA) in methylaluminoxane (MAO) and external alkylaluminum (AlR₃) 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 AlR₃, AlMe₃, AlEt₃, Al(i-Bu)₃, and AlEt₂Cl, into the catalyst systems are quite different, depending the properties of MAO used and the type of the external AlR₃. It was found that there is an optimum range of concentration ratio of the free AlR₃, including the residual TMA and external AlR₃, 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. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 765–770, 1998     

Lanthanide(II) amide complexes: Efficient initiators for the living polymerization of methyl methacrylate

Lanthanide(II) complexes supported by amido ligands, [(C₆H₅)(Me₃Si)N]₂Ln(DME)₂ [Ln = Sm ( 1 ) or Yb ( 2 ); DME = 1,2‐dimethoxyethane] and [(C₆H₃? ⁱPr₂‐2,6)(Me₃Si)N]₂Ln(THF)₂ [Ln = Sm ( 3 ) or Yb ( 4 ); THF = tetrahydrofuran], were found to initiate the polymerization of methyl methacrylate (MMA) as efficient single‐component initiators (in toluene for 3 and 4 and in toluene with a small amount of THF for 1 and 2 ) to produce syndiotactic polymers. The catalytic behavior was highly dependent on both the amido ligand and the polymerization temperature. Initiators 3 and 4 initiated MMA polymerization over a wide range of temperatures (20°C to ?40°C), whereas the polymerization with 1 and 2 proceeded smoothly only at low temperatures (≤0°C). The kinetic behavior and some features of the polymerizations of MMA initiated by 3 and 4 were studied at ?40°C. The polymerization rate was first‐order with the monomer concentration. The molar masses of the polymers increased linearly with the increase in the polymer yields, whereas the molar mass distributions remained narrow and unchanged throughout the polymerization; this indicated that these systems had living character. A polymerization mechanism initiated by bimetallic bisenolate formed in situ was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A single active site metal center of neodymocene chloride for the ring‐opening polymerization of ε‐caprolactone

A germyl‐bridged lanthanocene chloride, Me₂Ge(^tBu‐C₅H₃)₂LnCl (Ln = Nd; (Cat‐ Nd ), was prepared and successfully used as single catalyst to initiate the ring‐opening polymerization of ε‐caprolactone (ε‐CL) for the first time. Under mild conditions (60°C,[ε‐CL]/[Ln] = 200, 4 h), Cat‐ Nd efficiently catalyzes the polymerization of ε‐CL, giving poly(ε‐caprolactone) (PCL) with high molecular weight (MW) (>2.5 × 10⁴) in high yield (>95%). The effects of molar ratio of [ε‐CL]/Cat‐Nd, polymerization temperature and time, as well as solvent were determined in detail. When the polymerization is carried out in bulk or in petroleum ether, it gives PCL with higher MW and perfect conversion (100%). The higher catalytic activity of this neodymocene chloride could be ascribed to the bigger atom in the bridge of bridged ring ligands. Some activators, such as NaBPh₄, KBH₄, AlEt_3, and Al(i‐Bu)₃, can promote the polymerization of ε‐CL by Cat‐ Nd, which leads to an increase both in the polymerization conversion and in the MW of PCL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1212–1217, 2012     

Zur Polymerisation des Ethylens mit Vanadium(III)amid

Polymerization of Ethylene with Vanadium(III)amide By addition of AlEt₃, AlEt₂Cl or AlEtCl₂ to V(NPh₂)₃ · THF · 0,5 Dx. the polymerization of ethylene under normal conditions is started with increasing rate. The influence of the concentration of the catalyst components, the monomer concentration and the ageing time of the catalytic system on the rate is studied.     

Notable Effects of Aluminum Alkyls and Solvents for Highly Efficient Ethylene (Co)polymerizations Catalyzed by (Arylimido)‐ (aryloxo)vanadium Complexes

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium(V) complex, VCl₂(N‐2,6‐Me₂C₆H₃)(O‐2,6‐Me₂C₆H₃) ( 1 ), have been explored in detail. The activity of 5.84×10⁵ kg PE/mol V⋅h (TOF 2.08×10⁷ h⁻¹) has been achieved by 1 /EtAlCl₂ catalyst in CH₂Cl₂ at 0 °C, and the activity in toluene increased in the order: i‐Bu₂AlCl>EtAlCl₂>Me₂AlCl>Et₂AlCl> Et₂Al(OEt), AlEt₃, AlMe₃ (negligible activities). Both aluminum alkyl cocatalyst and solvent also affected the catalytic activity and the norbornene (NBE) incorporation in the ethylene/NBE copolymerization using complex 1 , whereas the NBE contents were not strongly affected by the kind of aryl oxide ligand in VCl₂(N‐2,6‐Me₂C₆H₃)(OAr) [OAr=O‐2,6‐Me₂C₆H₃ ( 1 ), O‐2,6‐i‐Pr₂C₆H₃ ( 2 ), O‐2,6‐Ph₂C₆H₃ ( 3 )].     

Effect of ZnCl2‐ and SiCl4‐doped TiCl4/MgCl2/THF catalysts for ethylene polymerization

In this research, ethylene polymerization was carried out in the presence of different additives (ZnCl₂, SiCl₄, and the combined ZnCl₂‐SiCl₄) on TiCl₄/MgCl₂/THF catalytic system. The presence of ZnCl₂‐SiCl₄ mixtures showed higher activity in ethylene polymerization when compared with the catalytic activity in the presence of single Lewis acids, ZnCl₂, or SiCl₄. The modified catalyst with ZnCl₂‐SiCl₄ demonstrated the highest activity, which was more than three times the activity of the system without Lewis acid modification. The enhanced activity can be attributed to the reduction in the peak intensity of MgCl₂/THF complexes with Lewis acid compounds as proven by XRD. This was reasonable because of some THF removal from the structure of MgCl₂/THF by Lewis acid compounds. In addition to the effect of modification with additives on the partial elimination of THF, the catalytic activities could be increased due to the titanium atoms that have been locally concentrated on the surface as seen by energy dispersive X‐ray spectroscopy measurement. On the basis of the in situ electron spin resonance measurement, the mixed metal chlorides (ZnCl₂‐SiCl₄) addition could promote the amount of Ti³⁺after reduction with triethylaluminum. It revealed that the modification of TiCl₄/MgCl₂/THF catalytic system with mixed metal chlorides (ZnCl₂‐SiCl₄) is very useful for ethylene polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1588–1594, 2013     

Preparation of highly active supported catalysts for producing polypropylene with less content of chloride

Summary Highly active supported catalysts for propylene polymerization have been prepared by treating the complexes of TiCl₃· 3C₅H₅N and MgCl₂·(THF) with AlEt₂Cl in the presence of MgO, Mg(OH) ₂ ^x or SiO₂. Polypropylene with less content or chloride was produced over these catalysts combined with AlEt₃.     

Polymerization of styrene using pyrazolylimine nickel (II)/methylaluminoxane catalytic systems

The polymerization of styrene with two pyrazolylimine nickel (II) complexes of (2-(C₃HN₂Me₂-3, 5)(C(Ph) = N(4-R₂C₆H₂(R₁)₂-2, 6)NiBr₂ (Complex 1 , R₁ = ⁱPr, R₂ = H; Complex 2 , R₁ = H, R₂ = NO₂)) activated by methylaluminoxane was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, and reaction time on catalytic activity and molecular weight of the polystyrene (PS) were investigated in detail. The electron-withdrawing of nitro group in Complex 2 could not enhance the catalytic activity for styrene polymerization; however, the molecular weights of polymers were increased. Both of the two catalytic systems exhibited high activity [up to 8.45 × 10⁵ gPS/(mol Ni h)] for styrene polymerization and provide PS with moderate to low-molecular weights (M_w = 2.21 × 10⁴∼ 5.71 × 10³ g/mol) and narrower molecular weight distributions about 2.0. The obtained PS were characterized by means of IR, ¹H NMR, and ¹³C NMR techniques. The results indicated that the PS was atactic polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Bis(cyclopentadienyl) lanthanide benzylthiolate: synthesis,molecular structure and catalytic property for ε-caprolactone –polymerization

Reaction of LnCl₃ first with three equivalent of C₅H₅Na in THF, then with one equivalent of benzyl mercaptan, led to complexes of [(C₅H₅)₂Ln(SCH₂Ph)]₂ (Ln?=?Sm(1), Yb(2)), being characterized by infrared spectra, elemental analyses and X-ray crystallography for 2. Complex 2 is a dimer with two thiolate ligands as bridging groups in eight coordinate. The Yb-S(benzyl) bonds in 2 (2.703(19) and 2.719(2) Å, respectively) were longer than the Yb-S(aryl) bonds (about 2.640 Å) in analogous complexes. The catalytic property for the polymerization of ε-caprolactone by 1 and 2 was studied. Similar experiment was also made with [(C₅H₅)₂Ln(SPh-p-CH₃)(THF)]₂ (Ln?=?Sm(3), Yb(4)) for comparison. It was found that complex 2 showed the activity best, and the activity decreased in the order of 2?>?3?>?1?>?4. When [ε-CL]₀/[Ln] was 500 and the polymerization temperature was 35°C, complex 2 catalyzed the polymerization in living character, which could not be achieved by lanthanide arylthiolates such as 3 and 4.     

Polymerization of styrene using novel bispyrazolylimine dinickel (II)/methylaluminoxane catalytic systems

The polymerization of styrene with a series of bispyrazolylimine dinickel (II) complexes of bis‐2‐(C₃HN₂(R₁)₂‐3,5)(C(R₂) = N(C₆H₃(CH₃)₂‐2,6)Ni₂Br₄ (complex 1 : R₁ = CH₃, R₂ = Ph; complex 2 : R₁ = CH₃, R₂ = 2,4,6‐trimethylphenyl; complex 3 : R₁ = R₂ = Ph; complex 4 : R₁ = Ph, R₂ = 2,4,6‐trimethylphenyl) in the presence of methylaluminoxane (MAO) was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, reaction time, and catalyst concentration on catalytic activity and molecular weight of the polystyrene were investigated in detail. The influence of the bulkiness of the substituents on polymerization activity was also studied. All of the four catalytic systems exhibited high activity (up to 10.50 × 10⁵ gPS/(mol Ni h)) for styrene polymerization and provide polystyrene with moderate to low molecular weights (M_w = 4.76 × 10⁴–0.71 × 10⁴ g/mol) and narrower molecular weight distributions about 2. The obtained polystyrene was characterized by means of FTIR, ¹H‐NMR, and ¹³C‐NMR techniques. The results indicated that the polystyrene was atactic polymer. The analysis of the end groups of polystyrene indicated that styrene polymerization with bispyrazolylimine dinickel complexes/MAO catalytic systems proceeded through a coordination mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Polymerization of butadiene and copolymerization of butadiene with styrene using neodymium amide catalysts

The polymerization of butadiene was performed with catalysts based on the complex Nd{N(SiMe₃)₂}₃ (1). This amide complex in combination with methyaluminoxane or with a boron compound ([HNMe₂Ph][B(C₆F₅)₄], [CPh₃][B(C₆F₅)₄] or B(C₆F₅)₃) and Al(iBu)₃ showed high activity and stereospecificity in polymerization of butadiene. The cationic complex [Nd{N(SiMe₃)₂}₂(THF)₂][B(C₆F₅)₄] (2) was prepared by reaction of 1 and [HNMe₂Ph][B(C₆F₅)₄]. The catalyst 2/Al(iBu)₃ (ratio Al/Nd: 10/1) was highly active for butadiene polymerization. Copolymerization of butadiene and styrene was performed with the catalytic system Nd{N(SiMe₃)₂}₃/[HNMe₂Ph][B(C₆F₅)₄]/Al(iBu)₃ (3). Copyright © 2004 Society of Chemical Industry     

Vinyl polymerization of norbornene with bispyrazolylimine dinickel(II)/methylaluminoxane catalytic system

The polymerization of norbornene has been investigated in the presence of two novel bispyrazolylimine dinickel(II) complexes bis-2-(C₃HN₂Me₂-3,5)(C(Ph) = N(4-RC₆H₄)Ni₂Br₄ (complex 1, R = H; complex 2, R = OCH₃) activated by methylaluminoxane. The two catalytic systems show high activity (up to 1.83 × 10⁶ gPNBE/(molNi·h)) for norbornene polymerization and provide polynorbornene (PNBE) with higher molecular weights (M _w = 4.44 × 10⁵–11.57 × 10⁵ g/mol) and narrower molecular weight distributions about 2.0. The electron-donating of methoxyl group in complex 2 could enhance the catalytic activity for norbornene polymerization, however, the molecular weights of polymers were decreased. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, reaction time and catalyst concentration on catalytic activity, and molecular weight of the PNBEs were investigated in detail. The obtained PNBEs were characterized by means of ¹H NMR, FTIR, and thermogravimetric analyses. The analyses results of PNBE indicated that the norbornene polymerization is vinyl-type polymerization rather than ring-opening metathesis polymerization.     

Selective activation of metallic center in heterobinuclear cobalt and nickel complex in ethylene polymerization

Heterobinuclear cobalt and nickel complex {2-[2,6-R₂-C₆H₃NC(CH₃)-(CH₃)CN-(3,5-R₂′)C₆H₂-CH₂-(3′,5′-R₂)C₆H₂NC(CH₃)]-6-[2,6-R₂-C₆H₃NC(CH₃)] pyridine}CoCl₂NiBr₂ (R = isopropyl) (N₅CoNi) was prepared by reaction of pentadentate nitrogen ligand containing 2,6-bis(imino)-pyridine and α-diimine moieties with CoCl₂ and NiBr₂(DME) in turn. The complex was applied as catalyst for ethylene polymerization activated by AlEt₃, MMAO and AlEt₃/[PhMe₂NH] [B(C₆F₅)₄] respectively. The performance of the heterobinuclear complex in ethylene polymerization was compared with corresponding mononuclear complexes (α-diimine nickel bromide and 2,6-bis(imino)-pyridine cobalt chloride) and their equivalent mixture (binary complexes). When the complex N₅CoNi was activated by AlEt₃ or MMAO, its ethylene polymerization activity was lower than its control, the binary complexes. Both heterobinuclear complex and binary complex produced PE with bimodal molecular weight distribution. The amount of high-molecular-weight polyethylene produced by nickel center of N₅CoNi was less than the binary complexes, which reveals that productivity of nickel center of N₅CoNi is selectively suppressed. When the heterobinuclear complex N₅CoNi is activated by AlEt₃/[PhMe₂NH][B(C₆F₅)₄], the relative productivity of nickel center increased, although the total activity of catalyst decreased compared with AlEt₃ as cocatalyst. With respect to AlEt₃, [PhMe₂NH][B(C₆F₅)₄] can preferably activate nickel center of heterobinuclear complex. The results suggest that metal site in the heterobinuclear complex is selectively activated by cocatalyst.     

Effects of tris(pentafluorophenyl)borane on the activation of zerovalent-nickel complex in the addition polymerization of norbornene

The effects of B(C₆F₅)₃ on the activation of the Ni(0) and Ni(II) complexes were studied in the polymerization of norbornene. The Ni(0) complex, such as bis(1,5-cyclooctadiene)nickel (Ni(COD)₂ (1), biacetylbis(2,6-diisopropylphenylimmine)(1,3-butadiene)nickel (2), or tetrakis(triphenylphosphine)nickel (5), in combination with B(C₆F₅)₃, was determined to have high activity in the polymerization of norbornene. On the other hand, the Ni(II) complex with B(C₆F₅)₃ did not provide any activity at all under analogous conditions regardless of the structure of the Ni(II) complex. The use of other borane compounds, such as B(C₆H₅)₃, BEt₃, and BF₃ etherate, with Ni(COD)₂ (1) in place of B(C₆F₅)₃ clearly showed the main functions of B(C₆F₅)₃. The high Lewis acidity of B(C₆F₅)₃ enabled it to activate catalytic complexes, thus inducing polymerization. The study of the ¹H, ¹³C, and ¹⁹F NMR spectra of the polynorbornene produced with Ni(COD)₂ (1) and B(C₆F₅)₃, in the presence or absence of ethylene, showed that the initiation of addition polymerization occurred through the insertion of the exo face of the norbornene into the Ni-C bond of the C₆F₅ ligand. A new polymerization mechanism was proposed in norbornene polymerization, wherein the active complex formed from Ni(COD)₂ (1) and B(C₆F₅)₃ acts as a catalyst.     

Controlled polyethylene chain growth on magnesium catalyzed by lanthanidocene: A living transfer polymerization for the synthesis of higher dialkyl-magnesium

The rare-earth metallocene chloride complexes (C₅Me₅)₂LnCl₂Li(OEt₂)₂ (Ln = Nd, Sm or Y) combined with an excess of dialkyl-magnesium compounds (butyl-ethyl-magnesium) afford active species for the polymerization of ethylene in alkanes or aromatic solvents at atmospheric pressure. A dynamic equilibrium between dormant species and a low concentration of catalytically active species is suggested to explain the living character of the polymerization process observed at temperatures up to 80 °C. A fluxional behavior of the polynuclear structure of the dormant species accounts for the fast and reversible exchange/transfer reaction of alkyl chains between lanthanide and magnesium metallic centers. The resulting mixture contains mainly di(polyethylenyl)magnesium compounds and can be directly used either for block copolymerisation with polar monomers or for any classical Grignard-like reaction for the synthesis of functionalized polyethylenes.     

Vapor deposition polymerization of 1,9-bis(trimethylsilyloxy)[2.2]paracyclophane

Summary Vapor deposition polymerization of 1,9-bis(trimethylsilyloxy)[2.2]paracyclophane (Me ₃ SiO-PC) was carried out to obtain poly(7-trimethylsilyloxy-p-xylylene) (Me ₃ SiO-PPX) as a colorless tough film. The Me ₃ SiO-PPX film was successfully converted to poly(7-hydroxy-p-xylylene) (HO-PPX) film by the hydrolysis reaction in THF in the presence of hydrochloric acid.     

Syndiospecific Polymerization of Styrene Using Half-Titanocene Catalyst Covalently Supported on MgCl<Subscript>2</Subscript>/AlEt<Subscript>n</Subscript>(OEt)<Subscript>3-n</Subscript>

The novel half-titanocene catalyst bearing reactive functional amino group, η⁵-pentamethylcyclopentadienyltri(p-amino-phenoxyl) titanium [Cp^∗Ti(p-OC₆H₄NH₂)₃], was easily synthesized by the reaction of η⁵-pentamethylcyclopentadienyltrichloride titanium (Cp^∗TiCl₃) with p-amino phenol in the presence of triethyl amine (NEt₃). Cp^∗Ti(p-OC₆H₄NH₂)₃ covalently anchored on MgCl₂/AlEt_n(OEt)_3-n support obtained from the reaction of triethylaluminium (AlEt₃) with the adduct of magnesium chloride (MgCl₂) and ethanol (EtOH), has been investigated and used to catalyze syndiospecific polymerization of styrene. Influences of the support structure, cocatalyst, and the molar ratio of Al in methylaluminoxane (MAO) and Ti (Al_MAO/Ti) on catalytic activity, syndiotacticity and molecular weight of the resultant polystyrene were investigated. Compared with the corresponding Cp^∗Ti(p-OC₆H₄NH₂)₃ homogeneous catalyst, a considerable increase in activity and molecular weight of syndiotactic polystyrene (sPS) was observed for the Cp^∗Ti(p-OC₆H₄NH₂)₃-MgCl₂/AlEt_n(OEt)_3-n supported catalyst even at a relatively low Al_MAO/Ti ratio of 50, and the kinetics of polymerization was stable during the reaction process.     

Ethylene polymerization using nickel α-diimine complex supported on SiO2/MgCl2 bisupport

Nickel α-diimine complex [C₆H₅-NC(CH₃)C(CH₃)N-C₆H₅]NiCl₂ was impregnated on SiO₂/MgCl₂ bisupport, and ethylene polymerizations were carried out with alkylaluminum compounds as cocatalyst. Branched polyethylenes were prepared when heptane is used as solvent. Polymerization conditions such as modified method of bisupport, cocatalyst, Al/Ni ratio, temperature and nickel concentration had a pronounced effect on catalytic activity and properties of polyethylenes. The activity of 2.9×10⁵ g PE mol Ni h⁻¹ was obtained in the presence of AlEt₂Cl as well as the bisupport without AlEt₃ modification, Al/Ni ratio 80, nickel concentration 0.12 mmol/l and temperature 14 °C. Branching degree of polyethylenes increased with temperature, and molecular weight, melting point and crystallinity of polyethylenes decreased correspondingly. Polymerization temperature had a pronounced effect on branches distribution of polyethylenes. Content of methyl branch increased sharply with temperature, but long branches dropped quickly.     

Mononuclear versus dinuclear palladacycles derived from 1,3-bis(N,N-dimethylaminomethyl)benzene: Structures and catalytic activity

Mononuclear and dinuclear palladacycles derived from 1,3-bis(N,N-dimethylaminomethyl)benzenes, [{Pd(Cl)}2,6-(Me₂NCH₂)₂C₆H₃] (1) and [1-{Pd(H₂O)(Py)}-5-{Pd(OTf)(Py)-2,4-(Me₂NCH₂)₂C₆H₂]-(OTf) (2), were synthesized and their structures were fully characterized. Complex 1 is a pincer complex with η³-mer NCN phenyl backbone, complex 2 is a bispalladium(II) complex with 1,2- and 4,5- two C,N-ortho phenyl backbone. Whereas the pincer complex 1 acted as a poor catalyst on methanolysis of fenitrothion, complex 2 demonstrated high catalytic activity in the same reactions, but there is no synergetic effect between two palladium ions. The results clearly indicate that a dissociable co-ligand in the palladacycle compounds significantly promotes the catalytic methanolysis.     

Formation of a binuclear titanocene hydride–magnesium hydride carbyl-bridged complex in the (C5Me4Ph)2TiCl2/Mg/THF system

The reduction of (C₅Me₄Ph)₂TiCl₂ by magnesium in tetrahydrofuran affords a mixture of the diamagnetic doubly tucked-in titanocene complex (C₅Me₄Ph)[C₅Me₂(CH₂)₂Ph]Ti (1), the paramagnetic trinuclear Ti–Mg–Ti hydride bridged complex [(C₅Me₄Ph)₂Ti(μ-H)₂]₂Mg (2) and the paramagnetic binuclear titanocene hydride–magnesium hydride complex (C₅Me₄Ph)[C₅Me₄(o-C₆H₄)]Ti(μ-H)₂Mg(THF)₂ (3). The X-ray diffraction analysis of 3 revealed that the magnesium atom forms the σ-bond to the ortho-carbon atom of one of the phenyl rings and binds 2 molecules of THF.