π-Allyl nickel halide–oxygen system as a catalyst for polymerization of butadiene

The π-allyl nickel halide-oxygen system was found to be active as catalyst for stereospecific polymerization of butadiene. The catalyst from π-allyl nickel chloride or π-allyl nickel bromide yields the polymer of 90% cis-1,4 content with high activity, whereas the catalyst from π-allyl nickel iodide affords a polymer of 70% or less cis-1,4 content. The catalyst systems can be fractionated into two parts on the basis of solubility in benzene. It is concluded that the catalyst activity originates essentially from the benzene-insoluble nickel complex which is composed of oxygen, halogen, σ-allyl group, and nickel. The structure of growing polymer terminal is discussed in relation to the mechanism of the stereospecific polymerization.     

Polymerization by transition metal derivatives. XII. Factors controlling activity and stereospecificity in the 1,4 polymerization of butadiene by monometallic nickel catalysts

In the course of investigations of polymerization of diolefins by transition metal derivatives, we have synthesized various monometallic nickel coordination catalysts. The complexes were prepared by reacting 2,6,10-dodecatriene-1,12-diyl nickel with protonic acids; they were shown to initiate the stereospecific polymerization of 1,3-butadiene. The study of these catalysts showed the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate. Moreover, by adding various ligands, we were able to modify the behavior of the catalytic systems and to prepare either pure cis-1,4 or pure trans-1,4 or cis–trans equibinary polybutadienes, starting from the same complex and keeping a high 1,4 specificity. Some of these modifications were shown to be reversible.     

Polymerization of butadiene and vinyl ether with catalyst prepared from π-allyl nickel halide and organic peroxide

The π-allyl nickel halide–organic peroxide system has been found to be active as catalyst for the stereospecific polymerization of butadiene and polymerization of vinyl ether. Benzoyl peroxide is most effective. The catalyst from π-allyl nickel chloride or π-allyl nickel bromide and benzoyl peroxide yields predominantly cis-1,4 polymer with high activity, whereas the catalyst from π-allyl nickel iodide affords predominantly trans-1,4 polymer. The catalyst system can be divided into two parts, a benzene-soluble and a sentially insoluble component. It is concluded that the catalyst activity originates esbenzene-from the insoluble nickel complex which is composed of halogen atom, benzoyloxy group of conjugated structure, allyl group, and nickel. A structure is proposed for the complex.     

Polymerization of 1,3-butadiene on cobalt and nickel halides

Butadiene polymerizes to cis-1,4 polymer on irregularly stacked, halogen-deficient crystals of cobalt(II) or nickel(II) halides. Halogen is removed from the halides by heating the salts under high vacuum or by photolyzing them in the presence of butadiene. Intrinsic viscosity and solubility of the polymer reach a steady state during polymerization. Cobalt chloride produces polymer of higher intrinsic viscosity than nickel chloride, but polymerization on nickel chloride is faster. Catalytic activity is attributed to the presence of ≤0.1% of nickel and cobalt monohalides in the catalyst.     

Equimolecular binary polydines. V. Equibinary poly(cis-1,4–trans-1,4)butadiene from bis(π-allyl nickel trifluoroacetate)

The preparation of equibinary poly(cis-1,4–trans-1,4)butadiene was investigated in the presence of bis(π-allyl nickel trifluoroacetate) modified with suitable additional ligands. The behavior of the catalytic species in the polymerization reaction as well as the specific basic properties of the equibinary polybutadiene produced support obviously a regular distribution of the cis and trans isomers in the polymer chains.     

1,4 polymerization of isoprene by titanate catalyst systems

Titanates are versatile in the 1,4 polymerization of isoprene. The (R′O)₄Ti/RAlCl₂ catalyst gives either cis- or trans-1,4-polyisoprene, depending on the nature of both the titanate and the solvent. Primary titanates give cis-1,4-polyisoprene in both aliphatic and aromatic solvents. Secondary titanates give cis-polyisoprene in aliphatic solvents, and trans-1,4-polyisoprene in aromatic solvents. Tertiary titanates give trans-polyisoprene in both aliphatic and aromatic solvents. A mechanism is postulated which takes into consideration the role of the solvent. ESR studies of the various titanate–RAlCl₂ catalysts were made; the paramagnetic structures are related to polymerization mechanisms.     

Relationship between structures and activities of silver salt–organic halide catalyst systems for styrene polymerization

The rate of bulk polymerization of styrene initiated by silver salt–organic halide systems was measured at 0°C. Neither of the catalyst components initiated the polymerization when used alone, while combined catalysts containing both components initiated the polymerization in the case that the components reacted with each other with precipitation of silver halide. The rate in the early stage of the polymerization increased with an increase in reaction time. Plots of yield against the second power of time gave a linear relation in the early stage of the polymerization. The slope of the line was taken as a measure of catalytic activity. The catalytic activity was markedly influenced by the kinds of the components. The activities of silver perchlorate–organic halide systems increased in the following order of halides: chloride < bromide < iodide in most cases. The activities of silver perchlorate–organic chloride systems increased with a decrease in ionization potentials of the organic groups of the chlorides. The activities of silver salt–benzyl bromide systems increased with a decrease in the pK_a values of conjugate acids of silver salts. From these results, it was concluded that the facility of ionic dissociation of the catalyst components determined the activities.     

Stereoselective addition of carbamates to unsaturated systems by means of mercury(II) nitrate. Synthesis of saturated nitrogen-containing heterocycles

The aminomercuration of dienes with carbamates and mercury(II) nitrate affords, after in situ demercuration with sodium borohydride, stereoselectively saturated nitrogen-containing heterocycles. Thus, the corresponding amidomercuration-demercuration of 1,4- or 1,5-hexadiene, and diallyl ether gives respectively N-alkoxycarbonyl cis-2,5-dimethylpyrrolidines and trans-3,5-dimethylmorpholines. From 1,5-cyclooctadiene 9-alkoxycarbonyl-9-azabicyclo[3.3.1]- and [4.2.1]-nonanes (molar ratio ca. 1:1) are obtained. By amidomercuration-demercuration of N-allylurethane cis-N,N'-bis(ethoxycarbonyl)-2,5-dimethylpiperazine is obtained. The intermolecular amidomercuration of unsaturated systems results stereochemically opposite to the same aminomercuration process.     

Polymerization of butadiene with the NiCl2‐methylaluminoxane catalyst

The polymerization of butadiene (Bd) with the soluble and insoluble parts of the NiCl₂‐methylaluminoxane (MAO) catalyst was investigated. Both parts initiate the polymerization of Bd to give a high molecular weight polymer consisting of mainly cis‐1,4‐structure. The activity of the soluble part for the polymerization is higher than that of the insoluble part. We presume that NiCl₂ reacts with MAO to give a soluble alkyl‐nickel complex that shows high activity for the polymerization of Bd.     

Pyrolysis of polyisoprenes. I. Differentiation between natural and synthetic cis-1,4-polyisoprenes

Two methods of differentiating between natural rubber and synthetic cis-1,4-polyisoprenes have been examined. Both techniques depend on the presence of Ziegler-Natta catalyst residues in the synthetic polymers. The major pyrolysis product of cis-1,4-polyisoprenes at 350°C is 1-methyl-4-(1-methylethenyl)cyclohexene. This can undergo disproportionation to yield 1-methyl-4-(1-methylethyl)benzene and methyl-(1-methylethyl)cyclohexenes. It is this disproportionation reaction, catalyzed by Ziegler-Natta catalyst residues or by carbon black, that is responsible for the different product ratios obtained on pyrolysis of natural rubber and Ziegler-Natta catalyzed cis-1,4-polyisoprenes. Lithium alkyl-polymerized polyisoprenes undergo this secondary disproportionation reaction only in the presence of carbon black. Derivative thermogravimetric traces of black-filled sulfur vulcanizates of natural rubber and synthetic polyisoprenes are significantly different because polymerization catalyst residues promote cyclization of the polymer.     

Homo- and copolymerization of butadiene and styrene with neodymium tricarboxylate catalysts

Homo- and copolymerizations of butadiene (BD) and styrene (St) with rare-earth metal catalysts, including the most active neodymium (Nd)-based catalysts, have been examined, and the cis-1,4 polymerization mechanism was investigated by the diad analysis of copolymers. Polymerization activity of BD was markedly affected not only by the ligands of the catalysts but also by the central rare-earth metals, whereas that of St was mainly affected by the ligands. In the series of Nd-based catalysts [Nd(OCOR)₃:R = CF₃, CCl₃, CHCl₂, CH₂Cl, CH₃], Nd(OCOCCl₃)₃ gave a maximum polymerization activity of BD, which decreased with increasing or decreasing the pKa value of the ligands. This tendency was different from that for Gd(OCOR)₃ catalysts, where the CF₃ derivative led to the highest polymerization activity of BD. For the polymerization of St and its copolymerization with BD, the maximum activities were attained at R = CCl₃ for both Nd- and Gd-based catalysts. The copolymerization of BD and St with Nd(OCOCCl₃)₃ catalyst was also carried out at various monomer feed ratios, to evaluate the monomer reactivity ratios as r_BD = 5.66 and r_St = 0.86. The cis-1,4 content in BD unit decreased with increasing St content in copolymers. From the diad analysis of copolymers, it was indicated that Nd(OCOCCl₃)₃ catalyst controls the cis-1,4 structure of the BD unit by a back-biting coordination of the penultimate BD unit. Furthermore, the long range coordination of polymer chain by the neodymium catalyst was suggested to assist the cis-1,4 polymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 241–247, 1998     

Copolymerization of dienes with neodymium tricarboxylate-based catalysts and cis-polymerization mechanism of dienes

It was found that poly(butadiene), poly(isoprene), and poly(2,3-dimethylbutadiene) with high cis-1,4 content were obtained with Nd(OCOR)₃–(i-Bu)₃Al–Et₂AlCl catalysts (R = CF₃, CCl₃, CHCl₂, CH₂Cl, CH₃) in hexane at 50°C [cis-1,4 content: poly(BD), > 98%; poly(IP), ≥ 96%; poly(DMBD), ≥ 94%]. Copolymerization of IP and styrene (St) was carried out at various monomer feed ratios to evaluate the monomer reactivity ratio and cis-1,4 content of the diene unit and then to elucidate the cis-1,4 polymerization mechanism of IP. The cis-1,4 content of the IP unit in the copolymers decreased with increasing St content in the copolymers. The cis-1,4 polymerization was disturbed by incorporating St unit in the copolymers, since the penultimate St unit hardly coordinates to the neodymium metal, resulting in a decrease of the cis-1,4 content in the copolymers. That is, the cis-1,4 polymerization of IP is suggested to be controlled by a back-biting coordination of the penultimate diene unit. On the other hand, in the case of poly(BD-co-IP) and poly(BD-co-DMBD), the cis-1,4 content of the BD, IP, and DMBD units in the copolymers was almost constant (cis: 94–98%), irrespective of the monomer feed ratios and polymerization temperature. Consequently, the penultimate IP and DMBD units favorably control the terminal BD, IP, or DMBD unit to the cis-1,4 configuration through the back-biting coordination. For the monomer reactivity ratios, a clear difference was observed in each system: r_BD = 1.22, r_IP = 1.14; r_BD = 40.9, r_DMBD = 0.15. Low polymerizability of DMBD was mainly ascribed to the steric effect of the methyl substituents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1707–1716, 1998     

Polymerization of 1,3-Butadiene Catalyzed by Cobalt(Ⅱ) and Nickel(Ⅱ) Complexes Bearing Pyridine-2-imidate Ligands

Cobalt and nickel complexes (1a-1d and 2a-2d, respectively) supported by 2-imidate-pyridine ligands were synthesized and used for 1,3-butadiene polymerization. The complexes were characterized by IR and element analysis, and complex 1a was further characterized by single-crystal X-ray diffraction. The solid state structure of complex 1a displayed a distorted tetrahedral geometry. Upon activation with ethylaluminum sesquichloride (EASC), all the complexes showed high activities toward 1,3-butadiene polymerization. The cobalt complexes produced polymers with high cis-1,4 contents and high molecular weights, while the nickel complexes displayed low cis-1,4 selectivity and the resulting polymers had low molecular weights. The catalytic activities of the complexes highly depended on the ligand structure. With the increment of polymerization temperature, the cis-1,4 content and the molecular weight of the resulting polymer decreased.     

Linear polybenzyls. II. Lack of structure control in benzyl chloride polymerization

Polybenzyls were prepared from benzyl chloride with different catalysts and solvents and at different temperatures. A model compound reaction for the polymerization was studied by reacting benzyl chloride with an excess amount of diphenylmethane to determine the effect of reaction conditions on substitution distribution. The degree of branching of polybenzyl samples was characterized from the infrared absorption spectra by using peaks assigned to para and ortho disubstitution products and monosubstitution units. The degree of branching so obtained correlated well with the results from the model compound reactions and with the thermal stabilities of the polymers. Anthracene unit formation was also related to the isomer content, and addition of complexing agents such as SO₂ or tetranitromethane caused a reduction in branching during polymerization. An unusual glass transition behavior was observed in these polymers.     

Radiation-induced polymerization at high dose rate. IV. Chloroprene in bulk

Bulk polymerization of chloroprene was studied at 25°C in a wide does rate range. Variations of the rate of polymerization (R_p) and molecular weight as a function of does rate were essentially the same as those in several monomers that are capab;e of radical and cationic polymerizations. The polymerization proceeds with radical mechanism at low dose rate ans with radical and cationic mechanism concurrently at high dose rate. The number-average molecular weight of the high-dose-rate was ca. 2400. Microstructure of the polymers was mainly of trans-1,4 unit with small fraction of cis-1,4 and 3,4-vinyl unit. Fractions of the vinyl unit and the inverted unit in trans-1,4 sequence which increased at high does rate inflected the change of dominant mechanism of polymerization.     

Metal-containing initiator systems. IV. Polymerization of methyl methacrylate by systems of some activated metals and organic halides

A study of the polymerization of methyl methacrylate initiated by the binary systems of some activated metals and organic halides has been made. It was found that the initiator activities of these systems were greatly dependent on the kind and the preparation or activation method of the metals (i.e., oxidation potential, surface area, and purity), and also on the kind of organic halides (i.e., bond-dissociation energy of their carbon–halogen bonds). From the kinetic studies of the polymerization at 60°C with the system reduced nickel–carbon tetrachloride, the rate of polymerization was found to be proportional to the monomer concentration and to the square root of concentration of both nickel and carbon tetrachloride at the lower concentration range of carbon tetrachloride, indicating that the system induced the radical polymerization. A similar conclusion was also obtained from the copolymerization with styrene with this system at 60°C, i.e., the resulting copolymer composition curve was in agreement with that obtained with azobisisobutyronitrile (AIBN). The apparent overall activation energy for the methyl methacrylate polymerization with this system was estimated to be 7.5 kcal/mole, which was considerably lower than that with AIBN. On the basis of the results obtained, an initiation mechanism for the polymerization with these initiator systems is presented and discussed.     

Polymerization of (E)‐1,3‐Pentadiene and (E)‐2‐methyl‐1,3‐pentadiene with neodymium catalysts: Examination of the factors that affect the stereoselectivity

(E)‐1,3‐Pentadiene (EP) and (E)‐2‐methyl‐1,3‐pentadiene (2MP) were polymerized to cis‐1,4 polymers with homogeneous and heterogeneous neodymium catalysts to examine the influence of the physical state of the catalyst on the polymerization stereoselectivity. Data on the polymerization of (E)‐1,3‐hexadiene (EH) are also reported. EP and EH gave cis‐1,4 isotactic polymers both with the homogeneous and with the heterogeneous system, whereas 2MP gave an isotactic cis‐1,4 polymer with the heterogeneous catalyst and a syndiotactic cis‐1,4 polymer, never reported earlier, with the homogeneous one. For comparison, the results obtained with the soluble CpTiCl₃‐based catalyst (Cp = cyclopentadienyl), which gives cis‐1,4 isotactic poly(2MP), are examined. A tentative interpretation is given for the mechanism of the formation of the stereoregular polymers obtained and a complete NMR characterization of the cis‐1,4‐syndiotactic poly(2MP) is reported. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3227–3232     

Synthesis and characterization of polymers of 1,4-hexadienes

The homopolymerization of trans-1,4-hexadiene, cis-1,4-hexadiene, and 5-methyl-1,4-hexadiene was investigated with a variety of catalysts. During polymerization, 1,4-hexadienes undergo concurrent isomerization reactions. The nature and extent of isomerization products are influenced by the monomer structure and polymerization conditions. Nuclear magnetic resonance (NMR) and infrared (IR) data show that poly(trans-1,4-hexadiene) and poly(cis-1,4-hexadiene) prepared with a Et₃Al/α-TiCl₃/hexamethylphosphoric triamide catalyst system consist mainly of 1,2-polymerization units arranged in a regular head-to-tail sequence. A 300-MHz proton NMR spectrum shows that the trans-hexadiene polymer is isotactic; it also may be the case for the cis-hexadiene polymer. These polymers are the first examples of uncrosslinked ozone-resistant rubbers containing pendant unsaturation on alternating carbon atoms of the saturated carbon-carbon backbone. Polymerization of the 1,4-hexadienes was also studied with VOCl₃- and β-TiCl₃-based catalysts. Microstructures of the resulting polymers are quite complicated due to significant loss of unsaturation, in contrast to those obtained with the α-TiCl₃-based catalyst. In agreement with the literature, there was no discernible monomer isomerization with the VOCl₃ catalyst system.     

Replacement of benzene with regulators for the catalyzed polymerization of 1,3‐butadiene to high cis‐1,4‐polybutadiene

The polymerization regulators mesitylene and 1,3,5‐trimethoxybenzene were investigated as suitable substitutes for benzene in the cobalt(II) octanoate/diethylaluminum chloride/water‐catalyzed polymerization of 1,3‐butadiene to high cis‐1,4‐polybutadiene. The propagation rates were reduced by 50% with the inclusion of 18 mM mesitylene or 0.17 mM trimethoxybenzene. Mesitylene was found to be an inefficient polymerization regulator because it reduced the propagation rate by a combination of regulation and destruction of the active catalyst complex. Not only did trimethoxybenzene reduce the propagation rate by effective regulation at low concentration, it also increased the percentage activity of cobalt to 200%, indicating that two polymer chains were propagating simultaneously from each active center. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2244–2255, 2001     

Carbon-13 NMR of polybutadiene

By using the carbon-13 NMR technique, it is shown that there are no cis-1,4–trans-1,4 linkages in a n-BuLi-catalyzed polybutadiene. The polymer consists of “blocks” of cis-1,4 units and trans-1,4 units separated by isolated vinyl units. Preliminary evidence suggests this might also be true for other types of 1,3-diene polymerization. Some of the implications of this finding on the mechanism of polymerization are discussed. Tacticity triad distributions are readily determined in polybutadienes with high 1,2 addition contents.