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.     

Synthesis and structure of a “living” copolymer of propylene and 1,5-hexadiene

A soluble V(acac)₃/Al(C₂H₅)₂Cl system was found to polymerize 1,5-hexadiene to give a living polymer in toluene at ?78°C. Hydrogenation of poly(1,5-hexadiene) was conducted to determine the chain microstructure. The ¹³C NMR analysis of hydrogenated poly(1,5-hexadiene) indicated that the poly(1,5-hexadiene) is composed of alternating units of 1,3-cyclopentylenemethylene and 1-vinyltetramethylene. In addition, living copolymers of propylene and 1,5-hexadiene were prepared and characterized by analysis of the ¹H and ¹³C NMR spectra. A chain propagation mechanism of living poly(1,5-hexadiene) is proposed.     

Regiospecificity of titanium-based catalyst system for propene polymerization

The sequence distribution of inverted monomeric units in the stereoirregular polypropylenes, prepared with the TiCl₄/Al(C₂H₅)₃ catalyst system, has been examined by ¹³C NMR. Observed dyad and triad sequence distributions were in good agreement with those calculated from first-order Markov statistics. The regioselectivity of an inserting propene seems to depend not only on the polarity of the active carbon-titanium bond but also on the steric effects of the last propylene unit of a growing chain.     

Mechanism of chain propagation in “living” polypropylene synthesis. 1H and 13C NMR analyses of chain-end structures

The mechanism of chain propagation in the living coordination polymerization of propene initiated by the soluble V(acac)₃/Al(C₂H₅)₂Cl catalyst was studied by ¹H and ¹³C NMR analyses of iodine-terminated polypropylenes of low molecular weights (M _n = 630 to 3200). A vanadium-carbon bond in the living polypropylene end reacts quantitatively with the iodine molecule to yield a new iodine-polymer bond. The ¹H and ¹³C NMR analyses of iodine-bonded polypropylene provide direct evidence on the stereochemistry of the first and last inserted propylene units and the structure of the living polypropylene end.     

13C NMR analysis of chemical inversion in polypropylene

Several new peaks observed in the ¹³C NMR spectra of polypropylene prepared with a VCl₄/Al(C₂H₅)₂Cl catalyst were assigned to the chemical inversion in the chain such as an isolated head-to-head or tail-to-tail unit.     

Coordination polymerization of lactides, 2. Microstructure determination of poly[(L,L-lactide)-co-(ε-caprolactone)] with 13C nuclear magnetic resonance spectroscopy

A detailed analysis of the structure of poly[(L ,L -lactide)-co-(ε-caprolactone)]

1 IUPAC-preferred name is dilactide:

was performed by means of high resolution ¹³C NMR (75 MHz) spectroscopy. The polyesters were obtained using various comonomer ratios and initiators aluminium tris(acetylacetonate) or the system Al(C₂H₅)₃ + Zn(C₂H₅)₂ + H₂O. Signals in spectra were assigned to appropriate structural sequences. Two types of chain structure containing different sequences and depending on the initiator used in copolymerization were found.     

Copolymerization of Ethylene and 1,7‐Octadiene, 1,9‐Decadiene with Zirconocene Catalysts

Copolymerizations of ethylene and 1,7‐octadiene (OD) and 1,9‐decadiene (DD) were investigated with various non‐bridged and bridged zirconocene catalysts using methylisobutylaluminoxane as a cocatalyst. The resulting copolymers were extracted with boiling o‐dichlorobenzene (ODCB), and the structure of the boiling ODCB‐soluble part was studied by ¹H, ¹³C NMR and DEPT (distortionless enhancement of polarization transfer) spectroscopy. In the case of ethylene/OD copolymerization, the ligand structure of the zirconocene catalysts strongly affected the propagation mode of OD. The zirconocene catalysts having cyclopentadienyl or pentamethylcyclopentadienyl ligands gave copolymers having 1‐hexenyl and 1,3‐disubstituted cycloheptane units, derived from 1,2‐addition propagation and addition–cyclization propagation of OD, respectively. On the other hand, the zirconocene catalysts with indenyl ligand produced the copolymers having exclusively 1,3‐disubstituted cycloheptane units. Furthermore, the copolymer prepared by diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride was crosslinked. The diastereostructure of the 1,3‐disubstituted cycloheptane units in the copolymers was not influenced by the stereospecificity of the catalysts used, and a cis‐structure was preferentially formed. In the case of the copolymerization of ethylene and DD, the C_2V‐symmetric zirconocene catalysts produced the copolymers with 1‐octenyl branches derived from 1,2‐addition propagation of DD. Other C₂‐ and C_S‐symmetric zirconocene catalysts with bulky ligands yielded copolymers with crosslinking structures derived form addition propagation of side‐chain unsaturated bond of 1,2‐added DD units.

Zirconocene catalysts used in the present investigation.     

The influence of the Ti3+ species on the microstructure of ethylene/1-hexene copolymers

Copolymerization of ethylene and 1-hexene was carried out with catalysts having isolated Ti³⁺ and multinuclear Ti³⁺ species. Carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR), crystallization analysis fractionation (CRYSTAF), and gel permeation chromatography (GPC) studies showed that the microstructure of ethylene and 1-hexene copolymers strongly depends upon the structure of the Ti³⁺ species. Isolated Ti³⁺ species increase the relative reactivity of ethylene in copolymerizations and produce copolymers with high molecular weight and broad short chain branching distribution (SCBD), with a large ethylene-rich fraction. Multinuclear Ti³⁺ species increase the relative reactivity of 1-hexene and produce copolymers with low molecular weight and broad SCBD, with a large rubbery ethylene/1-hexene fraction. Comparative studies of the copolymer microstructure from isolated Ti³⁺ and multinuclear Ti³⁺ in combination with different cocatalysts, Al(CH₃)₃ , Al(C₂H₅)₃ , and methylaluminoxane (MAO) were also carried out. Isolated Ti³⁺ species in combination with MAO cause remarkable changes in the 1-hexene incorporation rate and SCBD in comparison with Al(CH₃)₃ and Al(C₂H₅)₃ , while multinuclear Ti³⁺ species in combination with MAO do not affect as much the 1-hexene incorporation rate. This difference may be related to the mechanism of active site formation between the different Ti³⁺ structures and MAO.     

Effect of Et3Al and 9,9‐Bis(methoxymethyl)fluorine on Propylene Polymerization at High Temperature with TiCl4/MgCl2 Catalysts

Summary: A study of the effect of Et₃Al and a diether, 9,9‐bis(methoxymethyl)fluorine (BMMF), on propylene polymerization at high temperature with the use of MgCl₂‐supported catalysts is reported. BMMF could be extracted from a TiCl₄/MgCl₂/BMMF catalyst by Et₃Al at 100 °C, and Et₃Al is an efficient chain‐transfer agent in the presence of BMMF at 100 °C. The results obtained from differential scanning calorimetry (DSC) and ¹³C NMR spectroscopy showed that the isotactic poly(propylene) (iPPs) produced by the catalysts containing BMMF as an internal or external donor, contained ethylene units. This phenomenon was not found in the iPP chains obtained with donor‐free TiCl₄/MgCl₂ catalyst in the absence of any external donor at 100 °C. It is suggested that the decomposition of Et₃Al did not take place in the absence of any donor and took place in the presence of BMMF at 100 °C.

¹³C NMR spectrum of an iPP sample.     

Copolymerization of carbon dioxide with propylene oxide catalyzed by poly(p-hydroxystyrene)/diethylzinc system

A polymeric catalyst prepared from poly[1-(4-hydroxyphenyl)etylene] ( 1 ), and Zn(C₂H₅)₂ was found to be effective for the copolymerization of carbon dioxide and 1,2-epoxypropane. The highest activity was observed when a mole ratio of phenolic hydrogen in 1 to Zn(C₂H₅)₂ equal to unity was applied in contrast to the catalysts so far reported. The structure of the catalyst after the copolymerization was determined by IR and H¹ NMR spectroscopy. A Zn—C₂H₅ bond in this system was confirmed to be the active center. A possible inactivation process of the catalyst is proposed.     

Cross polarization/magic angle spinning 13C solid state nuclear magnetic resonance of model compounds related to supported ziegler-natta catalysts

Cross polarization/magic angle spinning ¹³C NMR has been applied to the investigation of some solid organometallic compounds of the general formulae TiCl₄ · n RCOOR′, MgCl₂ · n RCOOR′ (RCOOR′ = p-CH₃? C₆H₄COOCH₃ and C₆H₅COOC₂H₅, n = 1; 2; and 0,15). Compounds with n = 1 and 2 show narrow resonance lines indicative of crystalline regular structures while for MgCl₂ · 0,15 RCOOR′ a disordered structure is found with the organic ligands strongly bonded to the surface of MgCl₂ crystallites. For n = 2 splitting into a doublet is found for some resonances due to the spatial non-equivalence of the two ligands induced by crystalline packing. A shift has been found for some resonances in going from Mg to Ti complexes which reflects the different Lewis acidity of the two metal atoms.     

Metal-containing initiator systems, 34. Polymerization of vinyl monomers initiated by the binary system cobaltocene/bis(ethyl acetoacetato)copper (II)

The effect of some metallocenes such as ferrocene (Fe(C₅H₅)₂), nickelocene (Ni(C₅H₅)₂), and cobaltocene (Co(C₅H₅)₂), on the vinyl polymerization initiated with bis(ethyl acetoacetato)-copper(II) (Cu(eacac)₂) was investigated. Co(C₅H₅)₂ was found to exert a markedly accelerating effect on the polymerization of methyl methacrylate (MMA) with Cu(eacac)₂. The polymerization of MMA with the system Co(C₅H₅)₂/Cu(eacac)₂ at 50°C was found to be fairly affected by the solvent used. The results of copolymerization of MMA with styrene (St) and the effect of hydroquinone (HQ) on the polymerization of MMA with Co(C₅H₅)₂/Cu(eacac)₂ showed that the polymerization proceeds via a radical mechanism. The polymerization of MMA with Co(C₅H₅)₂/Cu(eacac)₂ was studied kinetically in acetone. The overall activation energy of the polymerization was calculated to be 86,3 kJ/mol (20,6 kcal/mol). This value was somewhat higher than that (17,6 kcal/mol) obtained for the polymerization of MMA with Cu(eacac)₂ alone. The polymerization rate (R_p) is represented by the following equation: R_p = k[Co(C₅H₅)₂]^0,5 [Cu(eacac)₂]^0,2 [MMA]^1,3. The high order in monomer concentration suggests a participation of the monomer in the initiation process of this polymerization. This is supported by the examination of the ESR spectrum of the system Co(C₅H₅)₂/Cu(eacac)₂/MMA/acetone, where reduction of Cu(II) to Cu(I) occurs. To elucidate the initiation mechanism, the spin trapping technique was applied to the system Co(C₅H₅)₂/Cu(eacac)₂/methyl acrylate. From these results, an initiation mechanism for the binary initiator system Co(C₅H₅)₂/Cu(eacac)₂ is proposed and discussed.     

Long‐Chain Branching and Rheological Properties of Ethylene‐1‐Hexene Copolymers Synthesized from Ethylene Stock by Concurrent Tandem Catalysis

Summary: Concurrent tandem catalysis systems have shown a significant advantage in the convenient synthesis of linear low‐density polyethylene (LLDPE) from a sole ethylene monomer stock by uniquely coupling the tandem action between an ethylene oligomerization catalyst and an ethylene copolymerization catalyst in a single reactor. Recently, we have reported the successful synthesis of ethylene‐hexene derived LLDPE using an effective concurrent tandem catalysis system comprising (η⁵‐C₅H₄CMe₂C₆H₅)TiCl₃ ( 1 )/MMAO and a CGC copolymerization catalyst, [(η⁵‐C₅Me₄)SiMe₂(^tBuN)]TiCl₂ ( 2 )/MMAO. In this work, we report the results from an extensive study on the important rheological properties of LLDPE grades prepared with this tandem catalysis system. Two sets of LLDPE samples having different short‐chain branching density (SCBD) were prepared with the tandem catalysis system under various catalyst concentrations and at temperatures of 25 and 45 °C. The melt rheological properties of these polymers were evaluated using small‐amplitude dynamic oscillation measurements. These polymers have been found to possess typical rheological properties found in long‐chain branched (LCB) polymers, such as enhanced zero‐shear viscosity (η₀), improved shear‐thinning, elevated dynamic moduli, and thermorheological complexity, which indicate the presence of long‐chain branching in the polymers. The long‐chain branching density (LCBD) of the two respective sets of polymers were qualitatively compared and correlated to the polymerization conditions including catalyst ratio and temperature. This work represents the first study on the rheological properties of LLDPE synthesized with concurrent tandem catalysis, and it discloses another appealing feature of this unique approach—its ability to produce LCB LLDPE from a single ethylene monomer stock.

Synthesis of linear low‐density polyethylene (LLDPE) from ethylene using ethylene oligomerization catalyst and an ethylene copolymerization catalyst.     

Synthesis of α,ω-dialkenyl isotactic poly(propylene) using bis(4-methyl-3-pentenyl)zinc as a chain transfer reagent

Propene polymerization was conducted with the catalyst system composed of TiCl₃ and bis(4-methyl-3-pentenyl)zinc (BMPZ) in the absence or presence of Al(C₂H₅)₂Cl. The catalyst system with or without Al(C₂H₅)₂Cl gave isotactic poly(propylene) (PP) with a lower molecular weight as compared to the TiCl₃/Al(C₂H₅)₂Cl system. From the ¹H and ¹³C NMR analyses, it was found that the polymer produced with the TiCl₃/BMPZ catalyst possesses a 2,6-dimethyl-5-heptenyl group and a Zn-PP bond at the initial and terminal ends, respectively. The Zn-terminated end was then converted to a vinyl group by coupling with allyl bromide in the presence of N-methylimidazole to obtain isotactic PP having CC double bonds at both chain ends.     

Preparation of Spherical MgCl2‐Supported Late‐Transition Metal Catalysts for Ethylene Polymerization

Summary: Facile and effective immobilization of late‐transition metal catalysts, 2,3‐bis‐(2,6‐diisopropylphenyl)butane diimine nickel(ii) dibromide ( A ) and 2,6‐bis‐[1‐(2,4,6‐trimethylphenylimino)ethyl]pyridine iron(ii) dichloride ( B ), for ethylene polymerization has been achieved, using spherical MgCl₂ supports obtained by thermal dealcoholization of MgCl₂ · 2.56C₂H₅OH instead of using supports of type MgCl₂/AlR_n(OEt)_3?n. BET, XRD, IR, SEM, GPC, and DSC analyses indicate that the composition and structure of the supports, the activities of the supported catalysts, and the properties of the resultant polymers are strongly dependent on the dealcoholization temperature. The support SP‐3 obtained by treating MgCl₂ · 2.56C₂H₅OH at 170 °C for 4 h is very effective for immobilizing late‐transition metal Fe^II and Ni^II catalysts. Compared with the corresponding unsupported homogeneous catalysts, a significant increase in activity is observed for the SP‐3 supported catalysts in ethylene polymerization, and the kinetics of polymerization is stable during the reaction process. In addition, replication of the support morphology is found in final polymers.

Kinetic profiles of ethylene polymerization using SPC‐4, SPC‐5, and SPC‐6 under 1.0 MPa and at 70 °C.     

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.     

Analyses of Propene and 1‐Hexene Oligomers from Zirconocene/MAO Catalysts – Mechanistic Implications by NMR,SEC, and MALDI‐TOF MS

A series of Cp′(C₅H₅)ZrCl₂ and Cp′₂ZrCl₂ pre‐catalysts (Cp′ = C₅HMe₄, C₄Me₄P, C₅Me₅, C₅H₄^tBu, C₅H₃‐1,3‐^tBu₂, C₅H₂‐1,2,4‐^tBu₃) together with (C₅H₅)₂ZrCl₂ was used for the directed oligomerization of propene and 1‐hexene in comparative experiments. Oligomer characterization was carried out by ¹H NMR, SEC (GPC), MALDI‐TOF MS, cryoscopy and Raman spectroscopy. From ¹H NMR the nature and relative ratio of the double‐bond end group is determined together with M̄_n if every oligomer molecule contains such a double‐bond end group. Normally vinylidene double bonds (from β‐hydrogen elimination) are found. From ¹H NMR and MALDI‐TOF MS also vinyl end groups (from β‐methyl elimination) are observed in the case of oligopropenes with (C₄Me₄P)‐ (C₅H₅)ZrCl₂ and with the symmetrical methyl containing Cp′₂ZrCl₂ pre‐catalysts. The vinylidene/vinyl ratio depends on the ligand and increases from C₅HMe₄ (65/35) over C₄Me₄P (61/39) to C₅Me₅ (9/91). A comparison of M̄_n from ¹H NMR and SEC together with MALDI‐TOF MS shows that the phospholyl‐zirconocenes and (C₅HMe₄)₂ZrCl₂ also exhibit chain transfer to aluminium, thereby giving saturated oligomers.     

Syntheses and characterization of terminally functionalized polypropylenes

Functional polypropylenes having vinyl, phenyl or hydroxyl groups at the chain end were prepared by adding common monomers as butadiene, styrene and 1,2-epoxypropane, respectively, at ?78°C during the living coordination polymerization of propene with a soluble V(acac)₃/Al(C₂H₅)₂Cl catalyst. In addition, polypropylene with hydroxyl functions was prepared by an alternative method based on the hydrogenation of a polypropylene containing aldehyde functions with LiAlH₄. These new types of terminally functionalized polypropylenes were well-characterized by ¹H NMR analysis.     

Carbon-13 nuclear magnetic resonance studies of poly(N-vinylcarbazole)

The ¹³C NMR spectra of poly(N-vinylcarbazole), [poly(1-(N-carbazolyl)ethylene)], prepared under various polymerization conditions were measured at 25,03 MHz in 1,4-dioxane solution. The spectra were assigned by the chemical shifts and T₁ measurements of the polymers and N-ethylcarbazole as a model compound. The absorption of methylene and methine carbons varied by the polymerization methods. It was tentatively presumed that the polymers obtained by radical polymerization had syndiotactic-rich structures and the polymers prepared with BF₃O(C₂H₅)₂ isotactic-rich structures. The hindered internal rotation of the bulky carbazolyl group at the main chain of poly(N-vinylcarbazole) was also observed. The ¹³C NMR spectra indicated that the polymerization of N-vinylcarbazole with nitroethane proceeded by a radical mechanism while that with chloranil, (2,3,5,6-tetrachloro-1,4-benzoquinone), proceeded by a cationic mechanism.     

Study of the mechanism of propagation and transfer reactions in the polymerization of olefins by Ziegler-Natta catalysts, 2. The influence of polymerization temperature on the kinetic characteristics of propagation

By quenching polymerization with radioactive carbon monoxide (¹⁴CO) data on the number of propagation centers (C_p) and the propagation rate constant (K_p) were obtained for the ethylene and propene polymerization in the presence of titanium trichloride at different temperatures. The values of K_p for ethylene and propene polymerization were found to be 8,0·10⁵ e^?13/(RT) and 3,0·10⁵ e^?23/(RT) l mol^?1 S^?1, respectively (activation energies in kJ mol^?1). It was further found that at increasing polymerization temperature the steady-state concentration of propagation centers increased when using Al(C₂H₅)₃ and Al(C₂H₅)₂Cl as cocatalysts, whereas it did practically not change in the case of Al(isobutyl)₃. On the basis of these data several conclusions were drawn on the mechanism of propagation and the role of organoaluminium cocatalysts in this reaction.