Copolymerization of Norbornene and Styrene Catalyzed by a Series of Bis(β-ketoamine) Nickel(II) Complexes in the Presence of Methylaluminoxane

Summary Random copolymerization of norbornene with styrene was studied by using a series of late metal catalysts/MAO. The precatalysts used here are nickel complexes with b-ketoamine ligands based on pyrazolone derivatives. The copolymers obtained here suggest that only one type of active species is present. Copolymers were characterized by ¹³C NMR, Gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and FT-IR spectra. The analyses of the product by ¹H NMR and ¹³C NMR spectra gave the verification of “true” random vinyl addition copolymer. Varying the monomer feed ratio controlled the composition of the copolymers. A copolymerization reactivity ratio (r_NBE = 20.35 and r_Sty = 0.027) indicates a much higher reactivity of norbornene, which suggests a coordination polymerization mechanism. The solubility and processability of the copolymers are improved relative to polynorbornene and the thermostability of the copolymers is improved relative to polystyrene.     

Polymerization of styrene using bis(β‐ketoamino)nickel(II)/methylaluminoxane catalytic systems

Styrene (St) was polymerized in toluene solution by using bis(β‐ketoamino)nickel(II) complex as the catalyst precursor and methylaluminoxane (MAO) as the cocatalyst. The polymerization conditions, such as Al : Ni ratio, monomer concentration, reaction temperature, and polymerization time, were studied in detail. Both of the bis(β‐ketoamino)nickel(II)/MAO catalytic systems exhibited higher activity for polymerization of styrene, and polymerization gave moderate molecular weight of polystyrene with relatively narrow molecular weight distribution (M_w/M_n < 1.6). The obtained polymer was confirmed to be atactic polystyrene by analyzing the stereo‐triad distributions mm, mr, and rr of aromatic carbon C¹ in NMR spectrum of the polymer. The mechanism of the polymerization was also discussed and a metal–carbon coordination mechanism was proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Polymerization of methyl methacrylate with Ni(acac)2–methylaluminoxane catalyst

Polymerization of methyl methacrylate (MMA) with nickel(II) acetylacetonate [Ni(acac)₂] in combination with methylaluminoxane (MAO) was investigated. Ni(acac)₂ was found to be an effective catalyst for the polymerization of MMA. From a kinetic study of the polymerization of MMA with the Ni(acac)₂–MAO catalyst, the overall activation energy was estimated to be 15 kJmol⁻¹. The polymerization rate (R_p) was expressed as follows: R_p = k [MMA]^1.0[Ni(acac)₂–MAO]^0.6 (the MAO/Ni mole ratio was kept constant). The mechanism for the polymerization of vinyl monomers with the Ni(acac)₂–MAO catalyst is discussed. © 2000 Society of Chemical Industry     

Syndiotactic polymerization of methyl methacrylate with Ni(acac)<Subscript>2</Subscript>-methylaluminoxane catalyst

In this study, syndiotactic-rich poly(methyl methacrylate) (PMMA) is obtained by using a soluble nickle acetylacetonate [Ni(acac)₂] and modified methylaluminoxane (MMAO-3A) catalyst system under modest polymerization conditions. The main purpose of this work is concerned with the study of previous conflicting stereospecificity data. Types of MAO, temperature of polymerization, MAO/Ni(acac)₂ (Al/Ni) mole ratio, and various solvents have been investigated in the MMA polymerization. Particularly, high syndiotactic PMMA [(rr) > 91 %] has been obtained when MMAO-3A is used as cocatalyst with Al/Ni ratio of ca. 50 or polymerization temperature ca. 0 °C. As expected, the prepared syndiotacticity-rich PMMA has a higher glass transition temperature (T _g) within 120 ~ 127 °C. The details of the polymerization mechanism, especially in relation to the stereoregularity problems are under investigation.     

Effects of trisobutylaluminium on styrene polymerization with Ni(acac)2 /MAO/SiO2 catalyst system activated by methylaluminoxane

Summary Styrene polymerization with Ni(acac)₂/MAO/SiO₂ catalytic system was carried out in the presence of methylaluminoxane (MAO), triisobutylaluminum (TIBA) or MAO and TIBA mixture as activators. The catalytic system activated only by TIBA produced polymer with 53% of isotacticity. When the catalytic system was activated by a mixture of MAO and TIBA the polymer isotacticity increases as MAO concentration increases. In this case, the maximum of isotacticity was 59%. The polymer has presented lower molecular weight than the polymer obtained by MAO as activators and the polymer microstructure was not explained by Markov first-order model. In addition, ¹³C NMR spectra of the polymers obtained after extraction with MEK, have indicated that there are two active sites in this catalytic system. Received: 28 November 2001 / Revised version: 24 May 2002 / Accepted: 29 May 2002     

Comparative study of homogeneous and heterogeneous styrene polymerizations with Ni(acac)2/MAO catalytic system

Styrene polymerization was carried out with Ni(acac)₂/MAO and Ni(acac)₂/SiO₂/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type.     

Some studies on styrene polymerization using new systems prepared from coordination metal compounds ReBr(CO)3(3,3′-dimethyl-2,2′-biquinoline)-diphenylzinc with and without MAO systems

The monovalent rhenium compounds ReBr(CO)₃(3,3′-dimethyl-2,2′-biquinoline) (I) and ReBr(CO)₅ (II) could be used as catalysts in styrene polymerization after activation with diphenylzinc (Ph₂Zn) and methylaluminoxane (MAO). The catalytic activity shown by the I-Ph₂Zn-MAO system was dependent on the molar ratio between the components and the temperature of polymerization. Non stereoregular polystyrene (PS) was obtained under all experimental conditions. The resulting PS gave multimodal GPC traces suggesting the presence of different species capable of polymerizing styrene, possibly species resulting from MAO alone, I-Ph₂Zn and I-Ph₂Zn-MAO systems. Received: 26 June 1997/Revised version: 13 November 1997/Accepted: 21 November 1997     

Polymerization of norbornene using bis(β‐ketoamino)nickel(II)/MAO catalytic systems

The polymerizations of norbornene were investigated using a series of bis(β‐ketoamino)nickel(II) complexes( 1–6 ) in combination with methylaluminoxane (MAO) in toluene solution. The effects of catalyst structure, Al/Ni molar ratio, reaction temperature, and reaction time on catalytic activity and molecular weight of the polynorbornene were examined in detail. The electronic effect of the substituent around the imino group in the ligand is stronger than the steric bulk one on the polymerization activities, and the activities are in the order of 1 > 2 > 4 > 5 > 6 > 3 . The obtained polynorbornenes were characterized by means of ¹H‐NMR, ¹³C‐NMR, FTIR, TG, and WAXD techniques. The analyses results of polymers' structures and properties indicate that the polymerization reaction of norbornene runs in vinyl‐addition polymerization mode. The obtained polynorbornene was confirmed to be vinyl‐type and atactic polymers and showed good thermostability (T_dec > 458°C) and were noncrystalline but had short‐range order. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4172–4180, 2006     

Cocatalytic activities of methylaluminoxane prepared by direct water addition method in ethylene polymerization over Cp2ZrCl2

The characterization of ethylene polymerization behaviors catalyzed over Cp₂ZrCl₂/MAO homogeneous system using methylaluminoxanes prepared by the direct hydrolysis of AlMe₃ (Me=methy1) were reported. The MAO was prepared at the ratio of [H₂O]/[A1]=1 and 0.5 and at three different temperatures, i.e., −40, −60 and −80 °C. The polymerization rate was not decreased with polymerization time when the MAO prepared at the ratio of [H₂O]/[AlMe₃]=l at −60 °C was used as a cocatalyst regardless of the ratio of Al/Zr and the polymerization temperature. The polymerization rate drastically decreased with polymerization time above 60 °C in case of using MAO prepared at the ratio of [H₂O]/[AlMe₃]=l at −80 °C. However, in case of the MAO prepared at the ratio of [H₂O]/ [AlMe₃]=0.5 at −80 °C, the rate continuously increased with polymerization time at the polymerization temperature of 70 °C and 80 °C. The amount of MAO needed to activate Cp₂ZrC1₂ was larger than that of MAO prepared at the ratio of [H₂O]/[A1]=1. The viscosity molecular weight of polyethylene (PE) cocatalyzed with MAO prepared at the ratio of [H₂O]/[Al]=0.5 was lower than that of polyethylene obtained with MAO prepared at the ratio of [H₂O]/[A1]=1.     

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride ^tBu-L₂ZrCl₂/MAO have been studied. The data on the number of active centers (C_P) and propagation rate constants (k_P) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (M_w = (4-10) × 10³ g mol⁻¹) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the k_P value was found to be 54 × 10³ L mol⁻¹ s⁻¹ at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (M_w = (30-1300) × 10³ g mol⁻¹). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (k_P = 17 × 10³ L mol⁻¹ s⁻¹).     

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.     

Syndioselective propylene polymerization: Comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

The kinetics and stereochemical control of propylene polymerization initiated by syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium–methyl aluminoxane (1/MAO) and (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium–MAO (2/MAO) were investigated. The influence of MAO concentration and polymerization temperature (T_p) on polymerization kinetics and polypropylene properties, such as molecular weight, molecular weight distribution (MWD), and stereoselectivity, have been studied in detail. The activity of both catalytic systems is very sensitive to the concentration of MAO. The 1/MAO and 2/MAO catalysts record maximum activity when [Al]/[Zr] ratio is around 1300 and 2500, respectively. The activity and the degree of stereochemical control are also sensitive to T_p. The 2/MAO catalyst is much more thermally stable than 1/MAO catalyst; the former shows maximum activity at 80°C, whereas the latter shows maximum activity at 20°C. The cationic active species generated by 2/MAO is not so stereorigid as those by 1/MAO so that 2/MAO catalyst produces sPP of broad MWD (4.43–6.38) and low syndiospecificity at high T_p. When T_p is above 50°C, 2/MAO catalyst produces completely atactic polypropylene. The results of fractionation of sPP samples produced by 1/MAO and 2/MAO demonstrate that 1/MAO catalyst is characterized by uniform active sites, but 2/MAO is characterized by multiple active sites. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 973–983, 1998     

Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization

Summary Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed by modification with AlEt₂Cl. Metallocene catalyst supported on such sol-gel product and activated by MAO appeared to be most active among studied systems. Studied Cp₂ZrCl₂/MAO supported on silica-type sol-gel carrier allow to obtain polyethylene (at 50°C polymerization temperature) with yield up to 30·10⁶ g/(mol_Zr·h), molecular weight below 300 000 and MWD=2−4. Received: 4 September 2000/Revised version: 3 January 2001/Accepted: 3 January 2001     

Effect of reaction parameters on the polymerization of methyl methacrylate with nickel acetylacetonate/methylaluminoane

Polymerizations of methyl methacrylate (MMA) employing nickel acetylacetonate [Ni(acac)₂] as catalyst combined with methylaluminoxane (MAO) as cocatalyst were investigated. The main purpose of this work is concerned with the study of reaction parameters MMA polymerization. Temperature of polymerization, Al/Ni mole ratio, type of solvent, catalyst concentration and time dependence were examined. The influence of Lewis bases on the polymerization was also studied. The binary system Ni(acac)₂/MAO was the only one able to polymerize MMA at the conditions employed in this work. The cocatalytic activity of MAO was compared to those of common alkylaluminium compounds. The polymers were characterized by gel-permeation chromatography (GPC) and ¹³C-NMR techniques. Received: 20 August 1996/Revised: 4 December 1996/Accepted: 9 December 1996     

Norbornene polymerization and ethylene/norbornene copolymerization catalyzed by constrained geometry cyclopentadienyl-phenoxytitanium catalysts

Norbornene polymerization and ethylene/norbornene copolymerization were studied using constrained geometry complexes 2-(tetramethylcyclopentadienyl)-4,6-di-tert-butylphenoxytitanium dichloride (1), 2-(tetramethylcyclopentadienyl)-6-tert-butylphenoxytitanium dichloride (2), and 2-(tetramethylcyclopentadienyl)-6-phenylphenoxytitanium dichloride (3) as catalysts with AlⁱBu₃ and Ph₃CB(C₆F₅)₄ as cocatalysts. Polymerization results indicate that these catalyst systems are highly active for both the homopolymerization of norbornene and the copolymerization of ethylene with norbornene. The norbornene homopolymerization is vinyl addition polymerization. Ethylene/norbornene copolymers with high norbornene incorporation (>50%) were easily obtained with these catalyst systems by increasing the norbornene feed concentration. The produced polymers were characterized by ¹³C NMR, IR, DSC and GPC.     

Preparation of polynorbornene with β-diketonate titanium / MAO catalysts

Summary Polynorbornene was synthesized by β -diketonate titanium / MAO (methylaluminoxane) catalysts. The polymerization activity was up to 8 × 10³ g polymer/(mol Ti h). FT-IR, ¹H NMR, ¹³C NMR and WAXD analyses showed that the polynorbornenes contained both ring-opening metathesis (trans and cis) and addition polymer chain structures and they are amorphous. The portions of trans- and cis- double bonds decreased when the polymerization temperature and Al/Ti molar ratio decreased. In addition, using 1,2-dichlorobenzene, instead of toluene, as the polymerization solvent increased the activity and produced the polymer containing more cis-double bonds. The glass transition temperature of the elastic polymers ranged from 330°C ∼ 400°C. Received: 10 September 2001/Revised version: 15 October 2001/Accepted: 10 December 2001     

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.     

Syntheses and radical ring-opening polymerizations of 1,1-bis(hydroxymethyl)-2-vinylcyclopropane and 1,1-bis(methoxymethyl)-2-vinylcyclopropane

Homo- and copolymerizations of 1,5-hexadiene with ethene and styrene using halfsandwich metallocene catalyst Me₂Si(Me₄Cp)(N-tert.-butyl)TiCl₂/MAO (Cp = cyclopentadienyl, Me = methyl, MAO = methylalumoxane) were investigated. According to ¹³C-NMR spectroscopic microstructure analysis, cyclopolymerization of 1,5-hexadiene afforded randomly distributed cis- and trans-cyclopentane rings in the homo- and copolymer backbone. 1,5-hexadiene incorporation reached 52 mol-%. The ratio of vinyl side chains to cyclopentane rings was controlled by 1,5-hexadiene concentration, where low 1,5-hexadiene concentration promoted cyclopolymerization. Copolymer glass transition temperatures increased with increasing content of cyclic units in the backbone. Styrene was used successfully as termonomer in ethene/1,5-hexadiene polymerization, resulting in a semicrystalline terpolymer with cyclic and styrenic units in the polymer backbone. Received: 5 September 1996/Accepted: 11 November 1996     

Polymerization of vinyl chloride with butyllithiums and metallocene catalysts

Polymerizations of vinyl chloride (VC) with butyllithium (BuLi) and metallocene catalysts were investigated. In the polymerization of VC with BuLi, the activity for polymerization decreased in the following order; t‐BuLi > n‐BuLi > s‐BuLi. A polymer controlled structurally in the main chain was found to be synthesized from the polymerization of VC with BuLi. The molecular weights of polymers obtained in bulk polymerization were higher than those of polymers obtained in solution. A linear relationship of the M_n of the polymer and the polymer yields was observed. The M_w/M_n of the polymer did not change significantly during polymerization, although the M_w/M_n was around 2. Thermal stability of the polymer obtained with BuLi was higher than that of polymer obtained with radical initiators, as determined by TGA measurements. In the polymerization of VC with Cp*TiX₃/MAO (X: Cl and OCH₃) catalysts, polymers were obtained with both catalysts, although the rate of polymerization was slow. The Cp*Ti(OCH₃)₃//MAO catalyst in CH₂Cl₂ gave higher‐molecular‐weight polymers in a better yield than in toluene. From elemental analysis and the NMR spectra of the polymers, the Cp*Ti(OCH₃)₃/MAO catalyst gave polymers consisting of repeating regular head‐to‐tail units, in contrast to the Cp*TiCl₃/MAO catalyst, which gave polymers having anomalous units.     

Polymerization of ethylene to branched poly(ethylene)s using <Emphasis Type="Italic">ansa</Emphasis>-η<Superscript>5</Superscript>-monofluorenyl cyclohexanolato zirconium(IV) complex/methylaluminoxane

ansa-η⁵-Monofluorenyl cyclohexanolato zirconium complex 3 was shown to be active for the polymerization of ethylene when activated with methylaluminoxane (MAO) at 5 bar. Up to a polymerization temperature of 40 °C, 3/MAO resulted in linear poly(ethylene)s with saturated chain ends. However, at polymerization temperatures of 60, 80, and 100 °C, a mixture of branched poly(ethylene)s, linear α-olefins and long chain alkanes was obtained. The poly(ethylene)s produced at 80 and 100 °C exhibited a bimodal molecular weight distribution indicative of multiple active species. Very high molecular weight (M _v > 5 × 10⁵) linear poly(ethylene)s were obtained using 3/MAO at 25 °C.