Ethylene/propene copolymerization in the presence of the homogeneous catalyst system Ti(Oi-C3H7)4/Al(C2H5)2F

The behaviour of the homogeneous catalyst system Ti(Oi-C₃H₇)₄/Al(C₂H₅)₂F in ethylene/propene copolymerization was studied. The copolymer structure is discussed in view of the stereoregulation mechanism previously proposed for vanadium-based homogeneous catalyst systems.     

Influence of ethyl benzoate on copolymerization of styrene and 1-hexene with the titanium-based systems (α)-TiCl3(H) and TiCl3 · 1/3 AlCl3

The influence of ethyl benzoate (E.B.) on the copolymerization of styrene with 1-hexene, initiated by isospecific Ziegler-Natta catalysts α-TiCl₃(H)-AlEt₃ and TiCl₃ · 1/3 AlCl₃-AlEt₃ (mole ratio Al/Ti = 3), was examined. Ethyl benzoate was found to reduce the activity of the catalysts. In addition it leads, depending on the Ti catalyst, to opposite effects on the apparent reactivity order of the two monomers. Incorporation of styrene into the copolymers is reduced when E. B. is added to TiCl₃ · 1/3 AlCl₃-AlEt₃. On the contrary, a much higher incorporation of styrene is observed with α-TiCl₃(H)-AlEt₃ in the presence of E. B. For this system the calculated reactivity ratio varies strongly with increasing proportion of E. B.: for a mole ratio AlEt₃/E. B. = 3, r_S = 0,94 and r_H = 1,46 and for AlEt₃/E. B. = 2, r_S = 8 and r_H = 0,1. Changes in the stereoregularity of copolymers suggest that E. B. leads to an inhibition of the less stereospecific sites for TiCl₃ · 1/3 AlCl₃-AlEt₃, whereas its addition suppresses the stereospecificity of the α-TiCl₃(H)-AlEt₃ catalyst. Contributions of conventional cationic and/or radical processes to the copolymerization reaction were examined and may be ruled out.     

Polymerization of α-olefins in the presence of δ-TiCl3/Al(CH3)3: Chain propagation rate constants for ethylene and propene

The chain propagation rate constants for the polymerization of ethylene and propene in the presence of δ-TiCl₃/Al(CH₃)₃ at 22 °C are determined by means of a ¹³C NMR analysis of suitable block copolymers. The numerical values of the rate constants are compared with those previously reported.     

On the 1,4‐cis‐Polymerization of Butadiene with the Highly Active Catalyst Systems Nd(C3H5)2Cl·1.5 THF/Hexaisobutylaluminoxane (HIBAO), Nd(C3H5)Cl2· 2 THF/HIBAO and Nd(C3H5)Cl2·2 THF/Methyl‐aluminoxane (MAO) – Degree of Polymerization,Polydispersity, Kinetics and Catalyst Formation

The allylneodymium chloride complexes Nd(C₃H₅)₂Cl·1.5 THF and Nd(C₃H₅)Cl₂·2 THF can be activated by adding hexaisobutylaluminoxane (HIBAO) or methylaluminoxane (MAO) in a ratio of Al/Nd = 30 for the catalysis of butadiene 1,4‐cis‐polymerization. A turnover frequency (TOF) of about 20 000 mol butadiene/(mol Nd·h) and cis‐selectivity of 95–97% are achieved under standard conditions ([BD]₀ = 2 m, 35°C, toluene). Molecular weight determinations indicate a low polydispersity (M̄_w (LS)/M̄_n (LS) = 1–1.5), the formation of only one polymer chain per neodymium and the linear increase of the degree of polymerization (DP) with the butadiene conversion, as observed for living polymerizations. First indications of chain‐transfer reaction occur only at the highest conversion or degree of polymerization. The rate law r_P = k_P[Nd][C₄H₆]^1.8 is derived for the catalyst system Nd(C₃H₅)₂Cl·1.5 THF/HIBAO and for the system Nd(C₃H₅)Cl₂·2 THF/MAO the rate law r_P = k_P[Nd] [C₄H₆]² with k_P = 3.24 L²/(mol²·s) (at 35°C). Taking into account the Lewis acidity of the alkylaluminoxanes and the characteristic coordination number of 8 for Nd(III) in allyl complexes the formation of an η³‐butenyl‐bis(η⁴‐butadiene)neodymium(III) complex of the composition [Nd(η³‐RC₃H₄)(η⁴‐C₄H₆)₂(X‐{AlOR}_n)₂] is assumed to be a single‐site catalyst for the chain propagation by reaction of the coordinated butadiene via the π‐allyl insertion mechanism and the anti‐cis and syn‐trans correlation to explain the experimental results.     

Organoaluminum catalysts for polymerization reactions. The effect of metal hydroxides on the catalytic activity of the Al(C2H5)3/H2O system

The catalytic activity of the system Al(C₂H₅)₃/H₂O was investigated. Instead of pure water aqueous solutions of inorganic bases were reacted with Al(C₂H₅)₃ in toluene/diethyl ether media. A uniform soft gel-like product was readily obtained in this reaction (H₂O/Al(C₂H₅)₃ ～ 1.0–1.5) differing from the heterogeneous nature of the product obtained with pure water. The polymerization of acetaldehyde proceeded with higher stereo-regularity in this system Al(C₂H₅)₃/aqueous inorganic base. The polymerization behavior and the stoichiometric reaction between the catalyst and the monomer (ethyl acetate formation) indicate that there seem not to be significant differences in the active species of Al(C₂H₅)₃/aqueous inorganic base and Al(C₂H₅)₃/H₂O systems. Improved stereospecific polymerization in the presence of inorganic bases is discussed with respect to the formation of a cross-linked product in the Al(C₂H₅)₃/H₂O system in the preparation of the catalyst.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 4. The influence of 14CO contact time and mole ratio Al(C2H5)3/Ti on concentration of active sites in ethylene homo- and copolymerization

The effect of varying ¹⁴CO contact time upon the concentration of active centres C* in ethylene homopolymerization using the TiCl₄/MgH₂ · Al(C₂H₅)₃ catalytic system shows that the polymer radioactivity, and hence C*, increase sharply in the first sixty minutes of ¹⁴CO contact with the polymerization centres. For contact times longer than one hour, the polymer radioactivity continues to increase, but very slowly. Studies on the effect of the mole ratio Al(C₂H₅)₃/Ti on ethylene homopolymerization show that both the catalytic activity and C* increase sharply when increasing the mole ratio Al(C₂H₅)₃/Ti in the range from 5 to 20. When increasing the mole ratio Al(C₂H₅)₃/Ti above 50, C* tends to decrease very slightly. In ethylene/1-hexene copolymerization a similar effect of the mole ratio Al(C₂H₅)₃/Ti on the polymerization is observed. However, even though the catalytic activity in copolymerization is observed to be higher than in homopolymerization, at the same mole ratio Al(C₂H₅)₃/Ti, yet C* in both cases is found to be more or less the same.     

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

The 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.     

Polymerization of ethylene with Cr[OC(CH3)3]4/Al(C2H5)2Cl as catalyst modified with some metal chlorides

Polymerization of ethylene was carried out in toluene using the homogeneous catalytic system Cr[OC(CH₃)₃]₄/Al(C₂H₅)₂Cl, combined with various metal chlorides (MtCl_x). The polymerization activity was found to be strongly dependent upon the MtCl_x used. A clear correlation was found between the activity and the elctronegativity X(Mt^x+) of the metal ion in MtCl_x. MtCl_x containing metal ions with X(Mt^x+) < 8,5 (electronegativity of the active Cr²⁺) show a markedly increased activity, whereas those with X(Mt^x+) > 8,5 have a rather decreased activity. Thus, for example, the catalyst combined with MgCl₂ shows very high activity to give a linear polyethylene with a remarkably high molecular weight and narrow molecular weight distribution. A plausible mechanism for the enhancement of the activity by suitable MtCl_x is proposed on the basis of these results.     

Trägerkatalysatoren aus C12-allylnickel(II)-komplexen [Ni(C12H19)]X (X = SbF6, O3SCF3) und amorphem aluminiumfluorid in toluol als modell-katalysatoren für das technische katalysatorsystem Ni(octanoat)2/BF3·OEt2/AlEt3 zur 1,4-cis-polymerisation des butadiens

The η³, η², η²-dodeca-2(E), 6(E), 10(Z)-trien-1-yl-nickel(II) complexes [Ni(C₁₂H₁₉)]X (X = SbF₆, O₃SCF₃) were treated in toluene with amorphous aluminium trifluoride (which was prepared from AlEt₃ and BF₃ · OEt₂) in a mole ratio 1 : 10 to 20, forming a highly active catalyst for the 1,4-cis polymerization of butadiene. This catalyst is comparable in its activity and selectivity, and in the molar mass distribution of the polybutadiene, with the technical nickel catalyst Ni(O₂CR)₂/BF₃?OEt₂/AlE₃ developed by Bridgestone Tire Company thirty years ago. The existence of the C₁₂-allynickel(II) cation [Ni(C₁₂H₁₉)]⁺ on the AlF₃ support could be proved by FAB mass spectroscopic measurements. In agreement with our reaction model for the allyl nickel complex catalyzed butadiene polymerization, it is concluded that the technical nickel catalyst in its effective structure can be described as a polybutadienylnickel(II) complex co-ordinated to a polymeric fluoroaluminate anion via a fluoride bridge.     

Syndiotactic styrene‐butadiene block copolymers synthesized with CpTiX3/MAO (Cp = C5H5, X = Cl,F; Cp = C5Me5, X = Me) and TiXn/MAO (n = 3, X = acac; n = 4, X = O‐tert‐Bu)

Copolymers sPS‐B consisting of blocks of syndiotactic polystyrene (sPS) and polybutadiene (B) have been prepared using CpTiX₃ (Cp = C₅H₅, X = Cl, F; Cp = C₅Me₅, X = Me) and TiX_n (n = 3, X = acetylacetonate (acac); n = 4, X = O‐tert‐Bu) activated with methylaluminoxane (MAO). If proper conditions are used, copolymers containing a range of styrene and butadiene molar fractions can be prepared. Structural analysis of these copolymers by means of ¹³C NMR spectroscopy allowed the assignment of different monomer diads (SS, SB, BB; S = styrene, B = butadiene) and the calculation of reactivity ratio products r₁·r₂. Differential scanning calorimetry (DSC) analysis further confirmed the block‐like structure of these copolymers. The melting points (T_m) of syndiotactic styrene sequences decrease as the styrene molar fraction decreases, whereas the glass transition temperature (Tg) increases with decreasing butadiene molar fraction in the copolymer. The polydispersity values (M_w/M_n) determined by GPC suggest that these copolymers are produced by a single site catalyst.     

Isospecific Propylene Polymerization Using the [ArN(CH2)3NAr]TiCl2/Al(iBu)3/Ph3CB(C6F5)4 Catalyst System in the Presence of Cyclohexene

Propylene polymerization was carried out using the [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6‐iPr₂C₆H₃)/Al(iBu)₃/Ph₃CB(C₆F₅)₄ catalyst system in the presence of cyclohexene. It was found that isospecific polymerization is promoted by adding cyclohexene even at low propylene concentration. It was also indicated that a considerable number of isospecific active species retain the metal‐polymer bond. Based on this fact, isotactic poly(propylene)‐block‐poly(1‐hexene) could be obtained.     

Polymerization of aromatic aldehydes, 11. Polymerization of 3-(o-formylphenyl)propionaldehyde and o-phenylenediacetaldehyde

Polymerization of 3-(o-formylphenyl)propionaldehyde ( 4 ) and o-phenylenediacetaldehyde ( 5 ) were performed with several ionic catalysts. The cationic polymerization of 4 yielded polyacetals which contained a seven-membered cyclic unit ( 7 ) in mole fractions of 0,3–0,5. The uncyclized unit ( 6 ) contained the pendant aromatic aldehyde. Apparently, the aromatic aldehyde group reacted during the course of the intramolecular cyclization. Polymerizations of 5 with BF₃·O(C₂H₅)₂, lithium tert-butoxide, or Al(C₂H₅)₃-TiCl₄ as catalysts, similarly gave polyacetals containing a seven-membered cyclic unit ( 10 ) in mole fractions of 0,5–0,8. The extent of cyclization decreased with increase in temperature in the cationic polymerization, resulting in a difference of ?7,5 kJ mol^?1 (?1,8 kcal mol^?1) between the activation energy of intramolecular cyclization and that of intermolecular propagation. The polymerization with Al(C₂H₅)₃ as catalyst gave a polyester via propagation involving a hydride shift.     

Monomer-isomerization polymerization, 37. Effect of transition metal chlorides on monomer-isomerization polymerization of 2-butene with TiCl3/Al(C2H5)3 as catalyst

The effect of transition metal chlorides (MtCl_x) as isomerization catalysts was examined in the monomer-isomerization polymerization of cis-2-butene with TiCl₃/Al(C₂H₅)₃ as a catalyst. The isomerization and polymerization depend on both, MtCl_x and MtCl_x/TiCl₃ mole ratio. The rate of polymerization of 2-butene with TiCl₃/Al(C₂H₅)₃/MtCl_x (mole ratio Al/Ti = 3,0, Mt/Ti = 1,0) as catalysts decreases in the following order: NiCl₂ > CoCl₂ > FeCl₃ > None > MnCl₂ > CrCl₃. This order was found to be in a good agreement with the electronegativity of the metal atom in the chloride.     

The crystal structure of α-TiCl3 and the reticular disorder introduced by ball-milling

By X-ray powder diffraction methods the crystal structures of α-TiCl₃ and of the products obtained by dry ball-milling activation of this form were studied. TiCl₃ microcrystals show initially a structural disorder in the positions of titanium atoms and the successive mechanical activation introduces into the structure some stacking faults, mainly associated to ±60° rotations of the triple layers Cl? Ti? Cl. The structural investigation has been carried out by an accurate fit of observed X-ray patterns to those calculated in correspondence of structures containing well-defined disordered sequences and of likewise well-defined crystallite sizes. Like γ-TiCl₃ and MgCl₂, α-TiCl₃ is very sensitive to mechanical activation, which improves the performances of these three compounds when they are employed as catalysts, or supports for catalysts, in Ziegler-Natta polymerization processes.     

Zur Katalyse der stereospezifischen Butadienpolymerisation mit den Katalysatorsystemen aus Nd(η3-C3H5)3 · dioxan und methylaluminoxan (MAO) sowie Hexaisobutylaluminoxan (HIBAO)

The activation of the tris(allyl)neodymium complex Nd(η³-C₃H₅)₃ · dioxane with alkylaluminoxanes (MAO or HIBAO) results in highly selective catalysts for the 1,4-cis-polymerization of butadiene (cis-selectivity up to 80%). Under standard conditions (50°C, toluene), the turnover frequency (TOF) of the catalyst/MAO system amounts to 10–15000 mol butadiene/(mol Nd · h). Molecular weight determinations indicate the formation of only one polymer chain per neodymium center as in a living polymerization reaction, and for the catalyst/HIBAO system the rate law r_p = k_p [Nd][C₄H₆] with k_p = 8,7 · 10^?2 mol/(L · s) (at 25°C) has been derived. As the catalytically active species, a cationic monobutenyl neodymium(III) complex is discussed, which is stabilized through coordinative interaction with the counter anion as well as the growing polybutadiene chain. This cationic complex reacts under insertion with butadiene in a bimolecular fashion.     

The role of additives for the improvement of δ-TiCl3 catalyst performance

The influence of ethylaluminium compounds (AIEt₃ and AICIEt₂) modified by 2,6-di-tert-butyl-4-methylphenol (BHT), tributylamine (TBA) and triphenylphosphine (TPP) on the polymerization of propene was investigated using catalysts based on TiCI₃ modified by internal Lewis bases. Two catalysts were employed in this study, one (Cat. A) was prepared by the reduction of TiCI₄ complexed with dibutyl ether (DBE)—mole ratio DBE/TiCI₄ = 0,67—with AlClEt₂ and the other one (Cat. B) was prepared in the same way, but a second internal base (ethyl benzoate (EB)) was added in a mole ratio EB/TiCl₃ = 0,04. Activity and stereospecificity of the catalyst systems were strongly affected by these modified cocatalysts. The role of the modifiers is discussed.     

[(η5‐C5Me4)SiMe2(NtertBu)]TiCl2 as Pre‐Catalyst for the Copolymerisation of Ethylene with 5,7‐Dimethylocta‐1,6‐diene and with 3,7‐Dimethylocta‐1,6‐diene

[(η⁵‐C₅Me₄)SiMe₂(NtertBu)]TiCl₂ was used as catalyst in the presence of methylaluminoxane (MAO) for the copolymerisation of ethylene with 5,7‐dimethylocta‐1,6‐diene (5,7‐DMO) and with 3,7‐dimethylocta‐1,6‐diene (3,7‐DMO), two linear non‐conjugated dienes readily available from terpene feedstock. The effects of reaction temperature, Al/Ti mole ratio and diene concentration in feed on the polymerisation activity and on the incorporation rates of the diene were investigated. The structure of the polymer and the distribution of the comonomer along the chains were investigated through NMR and DSC.     

Synthesis of carboxy- and chloro-terminated poly(propylene)s using Zn(C2H5)2 as chain transfer reagent

Propene was polymerized with conventional and Solvay-type TiCl₃ combined with Al(C₂H₅)₂Cl using Zn(C₂H₅)₂ as a chain transfer reagent. The produced terminal Zn-carbon bonds of the polymer were reacted with carbon dioxide and chlorine in the presence of N-methylimidazole followed by hydrolysis to obtain terminally carboxylated and chlorinated poly(propylene) in approximately 50% yield.     

Polymerization of Ethylene Catalyzed by Iron Complex Bearing 2,6‐Bis(imine)pyridyl Ligand: 1H and 2H NMR Monitoring of Ferrous Species Formed via Catalyst Activation with AlMe3, MAO,AlMe3/B(C6F5)3 and AlMe3/CPh3(C6F5)4

¹H and ²H NMR spectroscopic monitoring of ferrous species formed via interaction of 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl]pyridineiron(II) chloride ( 1 ) with AlMe₃, MAO, AlMe₃/B(C₆F₅)₃ and AlMe₃/CPh₃ (C₆F₅)₄ is reported. At interaction of 1 with MAO in toluene solution, the new stable heterodinuclear neutral complexes with proposed structures LFe(II)(Cl)(μ‐Me)₂AlMe₂ and LFe(II)(Me)(μ‐Me)₂AlMe₂ are formed (L is initial tridentate ligand). Complex LFe(II)(Cl)(μ‐Me)₂AlMe₂ predominates at low Al/Fe ratios (less than 50), while LFe(II)(Me)(μ‐Me)₂AlMe₂ at high Al/Fe ratios (more than 500). Complex assigned to LFe(II)(Me)(μ‐Me)₂AlMe₂ can be prepared via interaction of 1 with AlMe₃. Activation of LFe(II)(Me)(μ‐Me)₂AlMe₂ by B(C₆F₅)₃ and CPh₃B(C₆F₅)₄ gives rise to formation of new complexes with proposed structures [LFe(μ‐Me)₂AlMe₂]⁺[MeB(C₆F₅)₃]^– and [LFe(μ‐Me)₂AlMe₂]⁺ [B(C₆F₅)₄]^–. Unexpectedly, the activity at ethylene polymerization was even higher for 1 /AlMe₃ than for 1 /MAO catalytic system. The co‐catalytic activity of MAO towards 1 dramatically decreased with the diminishing of AlMe₃ content in the composition of MAO. Activity of the catalyst 1 /AlMe₃ and the molecular structure of polyethylene produced do not change noticeably at the addition of B(C₆F₅)₃ to 1 /AlMe₃.These data allow to suggest, that active species of 1 /AlMe₃ and 1 /MAO systems are neutral methylated ferrous complexes but not cationic intermediates. Probably, complex LFe(II)(Me)(μ‐Me)₂ AlMe₂ is the closest precursor of these active species.     

Cationic polymerization of α·β-disubstituted olefins. Part XI. Polymerization of 2-chloroethyl propenyl ether catalyzed by BF3·O(C2H5)2

2-Chloroethyl propenyl ether (CEPE) was synthesized, and its cationic polymerizability by BF₃·O(C₂H₅)₂ and the steric structure of the resulting polymer were studied. In the polymerization in toluene at ?78°C, the rate of consumption of monomers decreased in the following order: cis-CEPE > 2-chloroethyl vinyl ether > trans-CEPE. The steric structure of the β-methyl group of the resulting polymer was determined quantitatively on the basis of the NMR spectrum of the β-methyl protons decoupled from β-methine protons. In the polymerization of CEPE in toluene at ?78°C, the polymer obtained from trans-CEPE was rich in threo-meso structure whilst cis-CEPE gave a polymer containing almost the same amount of threo-meso and erythro-meso structures. With methylene chloride as solvent, the amount of threo-meso structure increased and that of erythro-meso structure decreased for the polymer obtained from cis-CEPE. The steric structure of the polymer obtained from trans-CEPE was independent of the nature of the solvent used. The effect of polymerization temperature on the steric structure of the polymers was also investigated.