Preliminary results on ethylene/propene copolymerization in the presence of Cp2Ti(CH3)2/Al(CH3)3/H2O

Ethylene/propene copolymerizations were carried out in the presence of the catalyst system Cp₂Ti(CH₃)₂/Al(CH₃)₃/H₂O (Cp = cyclopentadienyl group), and the reactivity ratios r₁, r₂ were determined through the Fineman and Ross equation and via ¹³C NMR. A nearly alternating copolymer structure was pointed out. The yields as well as the molecular weights of the copolymers strongly decrease with increasing propene mole fraction in the copolymers.     

Alternating copolymerization of butadiene and propene with the catalyst VO(ONeo)2 Cl/Al(i-C4H9)3, 1

The influence of basic reaction parameters—the ratio of catalyst components, the composition of the monomer mixture and the temperature—on the progress of the copolymerization, the molecular weight and the molecular weight distribution as well as on the composition of the copolymers obtained is reported. Conversion data for the variation of the mole ratio of comonomers show a maximum for an [Al]/[V] mole ratio of approximately 7, whereas the molecular weight of copolymers is not significantly influenced. An increase in the molecular weight of the copolymers can be obtained by an increase of butadiene content in the monomer mixture. However, there is also an increasing incorporation of butadiene into the copolymer. Raising the temperature from ?60°C to 0°C results in a significant decrease in molecular weight, whereas the composition of the copolymers is not significantly changed.     

Kinetics of polymerization of 1,3-dioxepane with the Al(C2H5)3/H2O catalyst system

The kinetics of the polymerization of 1,3-dioxepane (DH) with the catalytic system Al(C₂H₅)₃/H₂O was studied. The dependence of the polymerization rate R₀ of the monomer DH(M) may be represented by the equation: The kinetic scheme which verifies the obtained results is that which takes into consideration in the starting period of the polymerization the existence of chain transfer to the monomer. The decrease of the polymerization rate and the diminishing of the intrinsic viscosity at high conversions points to the existence of chain transfer to the polymer in this stage of the reaction. The reaction rate constants of the chain transfer to the monomer are one order of magnitude higher than those of the transfer reaction to the polymer.     

Copolymerization of ethylene and propene with a TiCl4/MgCl2-Al(C2H5)3 catalyst system using a stopped-flow method

Copolymerization of ethylene with a small amount of propene was conducted with a TiCl₄/MgCl₂-Al(C₂H₅)₃ catalyst system using a stopped-flow method. With an increase in the polymerization time from 0,035 to 0,145 s, the copolymer yield increases linearly but the number-average molecular weight of the copolymer showed a tendency of saturation. The rate constants of the propagation reaction as well as the concentrations of active sites were estimated using these data. On the other hand, the ¹H NMR spectra of copolymer did not display the resonances due to C?C double bonds which should be formed by chain transfer with monomer and/or by β-hydrogen elimination. It was also found that the crystallinity of the copolymer decreases to a great extent upon incorporation of even a very small quantity of propylene units. From these results, it was concluded that the apparent rate of copolymerization is not controlled by monomer diffusion through the polymer films. Rather the transfer reaction with Al(C₂H₅)₃ might predominantly take place during the copolymerization.     

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.     

Propene polymerization with δ-TiCl3/AlCl(C2H5)2 and δ-TiCl3/Al(C2H5)3 catalyst systems, 1. Effect of external donors

The effect of ethyl benzoate (EB), diisobutyl phthalate (DIBP), dibutyl ether (DBE) and triethoxy(phenyl)silane (EPS) as third components on the propene polymerization with the catalyst systems δ-TiCl₃/AlCl(C₂H₅)₂ and δ-TiCl₃/Al(C₂H₅)₃ was investigated. The influence of external donors on the isotacticity, catalyst activity and average molecular weight (M _v) was tested. If external donors are employed, M _v decreases, the insoluble fraction in boiling isooctane increases and the catalyst activity is strongly influenced by the mole ratio external donor/TiCl₃. The results indicate that all external donors employed have the same qualitative effect on catalytic active centers.     

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.     

Kinetics of homogeneous butadiene polymerization catalyzed by TiI2Cl2/Al(iso-C4H9)3,

Kinetics of homogeneous butadiene polymerization initiated by TiI₂Cl₂/Al(iso-C₄H₉)₃ catalysts were studied at constant monomer concentration. A reaction mechanism involving fast initiation and living chains propagation with reversible deactivation of the active sites was developed. The active sites concentration and number average molecular weight during polymerization were calculated. The molecular weight distribution resulting from the assumed kinetic scheme was also considered. A method was developed to calculate number and weight average molecular weight of polymer at any moment after establishing of the deactivation-reactivation equilibrium. The experimental findings are consistent with the presumed reaction mechanism.     

Polymerization of propylene to syndiotactic polymer. III. Behaviour of the catalyst system VCl4-Al(C2H5)2Cl in the presence of lewis bases

Polymerizations of propylene to syndiotactic polymer have been carried out in the presence of the catalyst system VCl₄-Al(C₂H₅)₂Cl-anisole. The data obtained have been related to those previously reported concerning the catalyst system, VCl₄-Al(C₂H₅)₂Cl. It was thus possible to propose a mechanism of formation of the catalytic complexes and to put forward or confirm some hypotheses on their constitution. A polymerization mechanism is also proposed that can justify both the type of stereoregularity of the polymer and the variation of steric regularity on varying the polymerization conditions.     

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.     

Syndiospecific polymerization of styrene with the catalytic system [Ti2(OC2H5)8Cl]2Mg2(μ-Cl)2/methylaluminoxane compared with MgCl2-supported and unsupported Ti(OC2H5)4

As a part of our interest in the performance of [Ti₂(OC₂H₅)₈Cl]₂Mg₂(μ-Cl)₂ as Ziegler-Natta catalyst, the polymerization of styrene with a toluene solution of this compound and methyl-aluminoxane as cocatalyst was performed. It was found that the present catalytic system promotes the syndiospecific polymerization of styrene with high stereoregularity and the results were compared with those obtained with MgCl₂-supported or unsupported Ti(OC₂H₅)₄ catalysts. Determination of the titanium oxidation states and electron spin resonance (ESR) measurements both in the absence and in the presence of styrene were carried out for all the catalytic systems aimed at shedding some light on the nature of the active species.     

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.     

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.     

Polymerization of styrene with the VOCl3/Li(iC5H11) catalyst system

The polymerization of styrene with the VOCl₃/Li(iC₅H₁₁) catalyst system has been studied. Rates of polymerization fall sharply with increase in Li/V ratio; the molecular weights, however, show a maximum at Li/V = 1. Polymerization is first order with respect to catlyst as well as monomer concentrations. Activation energy was found to be 5.67 kcal/mole. Zinc diethyl acts as chain transfer agent. There was no effect of trans-stilbene on molecular weights as well as on rate of polymerization. Valence of vanadium at Li/V molar ratio 1 is 4.12 and it decreases with increase in ratio.     

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.     

The influence of the comonomer in the copolymerization of ethylene with α-olefins using C2H4[ind]2ZrCl2/methylaluminoxane as catalyst system

Copolymers based on ethylene with different incorporations of 1-hexene, 1-octene and 1-decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From ¹³C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene-comonomer-ethylene-comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1-hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄_w/M̄_n) of the copolymers is rather narrow and dependent on the concentration of the comonomer incorporated.