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.     

Highly Active Single‐Site Catalysts for the 1,4‐cis Polymerization of Butadiene from Allylneodymium(III) Chlorides and Trialkylaluminiums – A Contribution to the Activation of Tris(allyl)neodymium(III) and the Further Elucidation of the Structure‐Activity Relationship

To further elucidate the structure‐reactivity relationship in the allylneodymium complex‐catalyzed 1,4‐cis polymerization of butadiene, the following catalyst systems are investigated in toluene more thoroughly: Nd(C₃H₅)₂Cl·1,4‐dioxane, Nd(C₃H₅)Cl₂·2.5 tetrahydrofuran (THF)/5–30 AlMe₃ and preformed Nd(C₃H₄R)₃ in combination with 2 Ph₃CCl, 2 Ph₃CCl/5 AlEt₃; 2 AlMe₂Cl, 2 AlMe₂Cl/30 AlMe₃; 2 AlEt₂Cl and 2 AlEt₂Cl/10 AlEt₃. From the catalytic activity, cis selectivity, polydispersity, degree of polymerization as a function of conversion, as well as the comparison of theoretical and experimental chain length and kinetic analysis, essential conclusions can be drawn concerning the formation reaction and structure of the real catalyst complex and the course of the polymerization reaction. For the combinations of Nd(C₃H₄R)₃ with 2 AlMe₂Cl/30 AlMe₃, 2AlEt₂Cl and 2 AlEt₂Cl/10AlEt₃, the rate law r_P = k_P[Nd][BD]² is derived with the values for k_P of 3.4 (at 35°C), 2.0 and 1.5 L²/(mol²·s¹) (at 50°C), respectively. In each case the formation of a η³‐butenyl bis(η⁴‐butadiene)neodymium(III) complex [Nd(η³‐C₃H₄R)(η⁴‐C₄H₆)₂(ClAlR′₂C₃H₄R)₂] (R′ = Me, Et) is assumed. The insertion reaction proceeds according to the π‐allyl insertion mechanism, and the high cis‐selectivity in accordance with the anti‐cis and syn‐trans correlation is a consequence of the preferential η⁴‐cis coordination of butadiene.     

Polymerizations of butadiene with Ni(acac)2-methylaluminoxane catalysts

Polymerizations of butadiene (BD) with transition metals (MtX) and methylaluminoxane (MAO) catalysts were studied. Among the catalysts examined, nicke(II) acetylacetonate [Ni(acac)₂] in combination with MAO revealed the highest catalytic activities for the polymerization of BD, giving high molecular weight polymers consisting of mainly cis-1,4-units in the microstructure. With Ni(acac)₂-MAO catalyst, the overall activation energy for the polymerization of BD between 0°C and 60°C was estimated to be 18 kJ/mol. From a kinetic study, the rate equation for the polymerization of BD with the Ni(acac)₂-MAO catalyst at 30°C can be expressed as follows: R_p = [BD]^1.8 [Ni(acac)₂-MAO]^0.9. The polymerization mechanism of the polymerization of BD with the Ni(acac)₂-MAO catalyst is discussed.     

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.     

ESR determination of rate constants for the radical polymerization of methyl phenethyl itaconate

Phenethyl 2-(methoxycarbonylmethyl)acrylate (methyl penethyl itaconate) ( 1 ) was prepared and its polymerization with dimethyl 2,2′-azoisobutyrate ( 2 ) was investigated kinetically in benzene. The polymerization rate (R_p) was found to be expressed by R_p = k·[ 2 ]^0,5·[ 1 ]^1,8 (at 50°C). Further, a higher dependence of R_p (2nd order) on the concentration of 1 was observed at 61°C. The overall activation energy of the polymerization was calculated to be a low value of 50,3 kJ/mol. The initiator efficiency (f) of 2 was determined to be 0,48 to 0,22 at 50°Cand 0,50 to 0,28 at 61°C. f decreases with increasing monomer concentration due to the high viscosity of 1 . The poly( 1 ) radical is stable enough to be observable by ESR at high temperatures (50–60°C). Rate constants of propagation (k_p) and termination (k_t) were estimated using the poly( 1 ) radical concentration determined by ESR. k_p [6,0 to 121/(mol·s) at 50°Cand 7,1 to 15 1/(mol·s) at 61°C] shows a trend to increase with the concentration of 1 . On the other hand, k_t [2,9·10⁴ to 17·10⁴1/(mol·s) at 50°Cand 6,9·10⁴ to 45·10⁴1/(mol. s) at 61°C] decreases with increasing MPI concentration. This behavior is responsible for the high order with respect to monomer concentration. Copolymerization of 1 (M₁) with styrene (M₂) at 50°Cgave the following results: r₁ = 0,36, r₂ = 0,40, Q₁ = 0,82 and e₁ = + 0,59. Using the above results, the rate constants of the cross-propagations were estimated to be k₁₂ = 22 1/(mol·s) and k₂₁ = 308 1/(mol·s) at 50°C.     

Gas‐phase polymerization of 1,3‐butadiene with supported half‐sandwich‐titanium‐complexes

Using half‐sandwich‐titanium‐complexes polybutadiene (BR) can be produced with a particular microstructure of about 81% cis, 18% 1,2, and 1% trans units. A stirred bed reactor and a fluidized bed reactor were constructed for gas‐phase polymerization of 1,3‐butadiene by cyclopentadienyltrichlorotitanium (CpTiCl₃) on MAO (methylaluminoxane) impregnated silica (MAO/SiO₂). The major determinant of polymerization activity and molecular weight is the Al_MAO/Ti‐ratio on the carrier. Polymerization activity increases to 14 500 kg BR/(mol Ti*h) with a molecular weight of 1.9×10⁶ g/mol and the catalyst becomes noticeably more stable. Activity further increases when the CpTiCl₃ catalyst is prealkylated with small quantities of TIBA (triisobutylaluminium). Systematic methodological experimentation of the heterogenization suggests that a Ti(III)‐species is responsible for polymerization. The gas‐phase polymerization of 1,3‐butadiene reveals a rate of polymerization which is considerably greater than the equivalent rate in the homogeneous system. The polymers all have similar characteristics, pointing to the same active species. The microstructure of the polybutadiene produced was investigated by spectroscopic measurements and by hydration; a preference to block structures of 1,2‐units could not be established.     

Kinetic Peculiarities of Ethylene Polymerization over Homogeneous Bis(imino)pyridine Fe(II) Catalysts with Different Activators

Summary: Method of polymerization inhibition by radioactive carbon monoxide (¹⁴CO) has been used to determine the number of active centers (C_P) and propagation rate constant (k_P) for ethylene polymerization with homogeneous complex 2,6‐(2,6‐(Me)₂C₆H₃NCMe)₂C₅H₃NFeCl₂ (LFeCl₂), activated with methylalumoxane (MAO) or Al(i‐Bu)₃. With both activators the rate profile of polymerization was unstable: high activity [0.8 × 10³–1.5 × 10³ kg PE per (mol_Fe · h · atm) at 35 °C] of the initial period sharply decreases (sevenfold in 10 min). In the beginning of polymerization with the catalysts LFeCl₂/MAO and LFeCl₂/Al(i‐Bu)₃, the C_P values were found to be 8 and 41% of total Fe‐complex content in catalysts, respectively, and decreased 1.5–2‐fold in 9 min. As polymerization proceeds, the k_P value for LFeCl₂/MAO system decreases from 5 × 10⁴ to 1.5 × 10⁴ L · (mol · s)⁻¹ LFeCl₂/MAO, and for LFeCl₂/Al(i‐Bu)₃ system from 2.6 × 10⁴ to 0.82 × 10⁴ L · (mol · s)⁻¹. Data on the effect of polymerization time on polyethylene molar mass distribution are presented. Basing on the obtained results it was suggested that highly reactive, but unstable centers, dominating at short polymerization times, produce low‐molar‐mass polyethylene, while polyethylene with higher molar mass is produced by less active (low k_P) and more stable centers.

Data showing change in molar mass distribution of polyethylene with polymerization time.     

Die katalyse der 1,4-cis-polymerisation des butadiens mit dem kationischen C12-allylnickel(II)-komplex [Ni(C12H19)]SbF6

The catalytic properties of η³,η²η²-dodeca-2(E),6(E),10(Z)-trien-1-yl-nickel(II) hexafluoroantimonate are investigated in some detail. Under standard conditions the complex catalyses the polymerization of butadiene in toluene at room temperature with an extremely high activity of nearly 15000 mol C₄H₆/(mol Ni · h) and a cis selectivity up to 90%. The activity increases linearly with both the nickel and the butadiene concentration. No change in the selectivity and in the limiting viscosity number [n] has been found in the investigated range of concentration and temperature.     

Copolymerization of Ethylene with 1‐Hexene Using Sterically Hindered Tris(pyrazolyl)borate Titanium (IV) Compounds

The copolymerization of ethylene/1‐hexene was studied using {Tp^Ms}TiCl₃ ( 1 ) (Tp^Ms = hydridotris(3‐mesitylpyrazol‐1‐yl) and {Tp^Ms*}TiCl₃ ( 2 ) (Tp^Ms* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) com‐ pounds in the presence of methylaluminoxane at 65°C. For both catalysts it was observed that the productivities decreased with increasing the 1‐hexene concentration in the milieu exhibiting a negative comonomer effect. The highest productivities and 1‐hexene incorporations were achieved in the case of {Tp^Ms*}TiCl₃ catalyst system. The resulting copolymers were not soluble in TCB even at 165°C. 1‐hexene incorporations were very low: ca. 1.2 and 3.3 mol‐%, respectively for ( 1 ) and ( 2 ). The r₁ and r₂ parameters for both ( 1 ) and ( 2 )/MAO catalyst systems clearly indicated a strong tendency of these catalytic precursors to preferentially promote ethylene homopolymerization. According to X‐ray photoelectron spectroscopy, from the analysis of the Ti2p^3/2 peak, Tp^Ms* catalyst seems to present a stronger cationic character after MAO treatment, which can explain in part its higher catalyst activity.     

Effect of tert‐Butyl Chloride on the Isoprene Polymerization with Neodymium Isopropoxide/Diisobutylaluminum Hydride and Neodymium Isopropoxide/Methylaluminoxane Catalysts

The effect of tert‐butyl chloride (tBuCl) as a third catalyst component on the isoprene polymerization with neodymium isopropoxide (Nd(OiPr)₃)/diisobutylaluminum hydride (Al(iBu)₂H) and Nd(OiPr)₃/methylaluminoxane(MAO) catalysts was examined in heptane at a fixed [Al]/[Nd] ratio of 30 and reaction temperatures of 30 and 60 °C. The Nd(OiPr)₃/Al(iBu)₂H catalyst was inactive without tBuCl, i.e., at [Cl]/[Nd] = 0, while it showed the highest activity under the conditions of [Cl]/[Nd] = 3.0 and an addition order of {Al(iBu)₂H + tBuCl} + Nd(OiPr)₃ to yield polyisoprene with relatively low molecular weight (M _n ca. 5 × 10⁴), broad MWD (M _w/M _n ca. 5.4), and high cis‐1,4 content (ca. 96%) at 30 °C. On the other hand, the Nd(OiPr)₃/MAO catalyst was effective at [Cl]/[Nd] = 0, and the most active at [Cl]/[Nd] = 1.0–1.5 with an addition order of {Nd(OiPr)₃ + MAO} + tBuCl to afford polymer with high molecular weight (M _n ca. 8 × 10⁵), fairly narrow MWD (M _w/M _n ca. 1.6) and high cis‐1,4 content (ca. 94%) at 30 °C. Thus, the novel Nd(OiPr)₃/MAO/tBuCl system features high activity, high molecular weight, narrow MWD, and high cis‐1,4 stereospecificity, as compared with the conventional Nd(OiPr)₃/Al(iBu)₂H/tBuCl system.

Effect of the [Cl]/[Nd] mole ratio on the cis‐1,4 contents with Nd(OiPr)₃/Al(iBu)₂H/tBuCl catalyst. Curve a: at 30 °C, 180 min; curve b: at 60 °C, 90 min.     

Polymerization of L-lactide and ϵ-caprolactone in the presence of methyl trifluoromethanesulfonate

The cationic polymerization of L -lactide and ?-caprolactone initiated by methyl trifluoromethanesulfonate in nitrobenzene was studied. The monomer conversion and the average molecular weight decrease when the temperature increases. The kinetics constants for L -lactide and ?-caprolactone polymerizations are, respectively, equal to 1,7·10^?3 min^?1 and 1,60·10^?3 min^?1 at 50°C. The thermodynamic parameters were determined from the temperature dependence of the equilibrium monomer concentration. Thus for L -lactide and ?-caprolactone polymerization the enthalpy and entropy values are, respectively, equal to ΔH(L -lactide) = ?24,9 kJ/mol; ΔS(L -lactide) = ?25 J/(mol·K) and ΔH(?-caprolactone) = ?15,35 kJ/mol; ΔS(?-caprolactone) = ?35 J/(mol·K).     

Polymerization of Butadiene with V(acac)3‐Methylaluminoxane Catalyst

Full Paper: Polymerization of butadiene (Bd) with V(acac)₃‐methylaluminoxane (MAO) catalyst was investigated. The microstructure of the polymer was found to depend strongly on the polymerization conditions. High polymerization temperature and high MAO/V(acac)₃ mole ratios were preferential to produce cis‐1,4 structure. Two kinds of active species were presumed from the GPC measurement of the polymers; one gives a high molecular weight polymer bearing high cis‐1,4 content, another affords a low molecular weight polymer with high trans‐1,4 content. A Solvent effect was observed. A polymer consisting of mainly trans‐1,4 unit was produced in CH₂Cl₂ in contrast to toluene and n‐heptane in which polymers consisting of mainly cis‐1,4 structure were observed. The addition of ethyl benzoate, triethylamine, chloranil, and tetracyanoquinodimethane to the V(acac)₃‐MAO catalyst gave an influence to not only the activity for the polymerization but also the microstructure of the polymer.     

Ethylene Polymerization over Homogeneous and Supported Catalysts Based on Bis(imino)pyridine Co(II) Complex: Data on the Number of Active Centers and Propagation Rate Constant

The number of active centers (C_P) and propagation rate constant (k_P) for ethylene polymerization with homogeneous catalyst LCoCl₂ + MAO and supported catalyst LCoCl₂/SiO₂ + Al(i‐Bu)₃, where L is 2,6‐(2,6‐(Me)₂C₆H₃N = CMe)₂C₅H₃N, have been determined using the method of polymerization quenching by radioactive carbon monoxide (¹⁴CO). The unstable rate profile of the reaction was attributed to a decrease in the number of active centers from 0.23 to 0.14 mol · mol^?1(Co) corresponding to an increase in the reaction time from 5 to 15 min, whereas the k_P value remained constant, amounting to 3.5 × 10³ L · mol^?1 · s at 35 °C. A narrow molecular weight distribution of the obtained polyethylene (PE) samples ( = 1.9) testifies that the homogeneous catalyst LCoCl₂ + MAO can be regarded as a single‐site system. The activity of the supported catalyst was stable and noticeably lower than that of the homogeneous catalyst due to the low concentration of the active centers (0.02–0.03 mol · mol^?1(Co)). PE with a broad molecular weight distribution ( = 36) and noticeably higher molecular weight is formed in the presence of the supported catalysts. The activity of the supported catalyst increases sharply at polymerization in the presence of hydrogen. The data obtained on the C_P and k_P values allow suggesting the formation of the “dormant” centers at polymerization without hydrogen and regeneration of the active centers in the presence of hydrogen. The average k_P values for the supported catalyst containing multiple active centers were determined to be 5.9 × 10³ and 10.5 × 10³ L · mol^?1 · s, respectively, at 35 and 50 °C.

     

Role of bulky α-substituent in free-radical polymerization and copolymerization of methyl α-(alkoxymethyl)acrylates

Methyl α-(alkoxymethyl)acrylates were prepared from methyl α-(bromomethyl)acrylate in 80–90% yield. The monomers homopolymerize fast to yield low-molecular-weight polymers. The monomers bearing a linear alkoxymethyl group except for the ethoxymethyl group are characterized by a relatively low ceiling temperature. The rate constants for propagation k_p and termination k_t of methyl α-(butoxymethyl)acrylate were evaluated to be k_p = 298 dm³ · mol^?1 · s^?1 and k_t = 8 · 10⁶ dm³ · mol^?1 · s^?1 at 60°C, respectively. The α-(alkoxymethyl)acrylates are more reactive than methyl methacrylate toward polystyrene radical, except for the α-(dodecyloxymethyl)acrylate which is slightly less reactive, indicating that an increase in the reactivity by the electron-withdrawing character of the alkoxy group prevails over the steric hindrance against addition of the polymer radical, except for the large dodecyloxymethyl group.     

Solvent effect on the propagation rate constant in the radical polymerization of bis(2-ethylhexyl) itaconate

Polymerization of bis(2-ethylhexyl) itaconate ( 1 ) with dimethyl azobis(isobutyrate) ( 2 ) was carried out at 50°C in various solvents. Polar solvents caused a significant decrease in the polymerization rate (R_p) and the molecular weight of resulting poly( 1 ). The propagating poly( 1 ) radical could be observed as a five-line ESR spectrum in the actual polymerization systems used. The stationary concentration of poly( 1 ) radical was determined by ESR to be 4,2–6,4 · 10^?6 mol · L^?1 at 50°C when the concentrations of 1 and 2 were 1,03 and 3,00 · 10^?2 mol · L^?1. Using R_p the monomer concentration and the polymer radical concentration, the propagation rate constant (K_p) was estimated to be 1,4–6,8 L · mol^?1 · s^?1, depending on the solvents used. The k_p value was smaller in more polar solvents. The solvent effect is explained in terms of the solvent affinity for the propagating polymer chain.     

Kinetic and ESR studies of the radical-initiated polymerization of N-(2,6-dimethylphenyl)itaconimide

The polymerization of N-(2,6-dimethylphenyl)itaconimide (1) with azoisobutyronitrile (2) was studied in tetrahydrofuran (THF) kinetically and spectroscopically with the electron spin resonance (ESR) method. The polymerization rate (R_p) at 50°C is given by the equation: R_p = K [2] ^0,5 · [1] ^2,1. The overall activation energy of the polymerization was calculated to be 91 kJ/mol. The number-average molecular weight of poly (1) was in the range of 3500–6500. From an ESR study, the polymerization system was found to involve ESR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k_p) and termination (k_t) were determined at 50°C. k_p (24–27 L · mol^?1 · s^?1) is almost independent of monomer concentration. On the other hand, k_t (3,8 · 10⁴–2,0 · 10⁵ L · mol^?1 · s^?1) increases with decreasing monomer concentration, which seems mainly responsible for the high dependence of R_p on monomer concentration. Thermogravimetric results showed that thermal degradation of poly (1) occurs rapidly at temperatures higher than 360°C and the residue at 500°C was 12% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 50°C in THF the following copolymerization parameters were found; r₁ = 0,29, r₂ = 0,08, Q₁ = 2,6, and e₁ = +1,1.     

Cationic polymerizations initiated by high energy radiation

Ionizing radiations generate both free radicals and ions upon interaction with matter and under appropriate conditions either free radical or ionic polymerizations are observed. Cationic polymerizations are favored by the presence of halogenated solvents and by low reaction temperatures. Selective inhibitors and copolymerization studies make it possible to determine the relative proportions of the cationic and the free radical contributions to the overall process under a variety of experimental conditions (temperature, reaction medium, radiation dose-rate). Pure, carefully dehydrated hydrocarbon monomers undergo cationic polymerization when irradiated at room temperature. This reaction proceeds at a very high rate and is believed to involve free propagating cations. Propagation rate constants are available for the following monomers: styrene (k_p = 3,5·10⁶ at 15°C), α-methylstyrene (k_p = 4.10⁶ at 0°C), cyclopentadiene (k_p = 6.10⁸ at ?78°C), isobutene (k_p = 1,5·10⁸ at 0°C), and isobutyl vinyl ether (k_p = 3.10⁵ at 30°C). The present views on the mechanism of radiation induced cationic chain initiation and chain propagation are briefly discussed.     

Living polymerization of [o-(trifluoromethyl)phenyl]acetylene by a new catalyst system,MoOCl4–Et3Al–EtOH (1 : 1 : 4)

A new MoOCl₄-based living polymerization catalyst, MoOCl₄–Et₃Al–EtOH (mole ratio 1 : 1 : 4)/anisole, has been developed. Polymerization of [o-(trifluoromethyl)phenyl]acetylene by this catalyst in anisole at 30°C yielded a polymer having very narrow molecular weight distribution (M_w/M_n = 1,02), a four-fold excess of ethanol over MoOCl₄ was necessary to attain narrow molecular weight distributions. Multistage polymerization experiments clearly showed the living nature of the polymerization, which was maintained in the temperature range of 0 to 30°C. The absolute number-average molecular weight of the polymer measured by vapor pressure osmometry could be correlated with the number-average molecular weight measured by gel permeation chromatography as follows: M_n(VPO) = 1,48 × M_n(GPC). The propagation rate constant (k_p) at 30°C is 1,5 mol·L^–1·s^–1.     

Copolymerization of styrene and butadiene with Co(acac)3‐methylaluminoxane catalyst

The copolymerization of Styrene (St) and butadiene (Bd) with Co(acac)₃‐MAO catalyst was investigated. The copolymers consisting of St and Bd with highly cis‐1,4‐structure could be synthesized with Co‐(acac)₃‐MAO catalyst without formation of homopolymer, although the St contents in the copolymer were not high. The copolymer composition curve for copolymerization of St and Bd with the Co(acac)₃‐MAO is different from that obtained with the Ni(acac)₂‐MAO catalyst. The additive effects of triphenylphosphine (TPP) and trifluoroacetic acid (TFA) on the copolymerization of St and Bd with the Co(acac)₃‐MAO catalyst were also investigated. The copolymer yields increased by adding TPP to the Co‐(acac)₃‐MAO catalyst, although the St contents in the copolymer did not change. In the microstructure of the Bd units in the copolymers, 1,2‐contents increased remarkably. The copolymer yields and the microstructure of the copolymer did not change by addition of TFA.     

Novel Methylaluminoxane‐Activated Neodymium Isopropoxide Catalysts for 1,3‐Butadiene Polymerization and 1,3‐Butadiene/Isoprene Copolymerization

The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)₃] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)₃/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 10⁵ g mol^‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)₃/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).