Alternate Transition Metal Complex Based Diene Polymerization

Abstract

In the last decade, there has been a tremendous increase in the number of reports on transition metal complex-mediated butadiene homo- and copolymerization. While typical classical titanium, nickel, cobalt, and neodymium based catalysts have been almost exclusively applied to the production of high cis-1,4-polybutadiene, alternative catalyst systems are currently being developed which enable tuning of the polybutadiene microstructure and permit defined changes in polymer properties such as molecular weight distribution and changes in the polymer glass temperature. Besides new products such as high trans-1,4-polybutadiene or a polymer containing a defined amount of 1,2-polybutadiene, there are butadiene copolymers with different amounts of styrene, isoprene, or ethylene. These new materials should lead to new applications especially in the area of tires, high impact polystyrene (HIPS), and ABS. This review elucidates the new developments in the area of transition metal complex-based butadiene homo- and copolymerization focusing mainly on the transition metal catalyst, the polymerization process and the resulting polymers. Mechanistic details are discussed briefly and wherever useful for the understanding of the polymerization reaction.     

Nd(OR)3-mClm-AlEt3 catalyst system in the polymerization of butadiene: I. The general feature of polymerization

Homopolymerization of butadiene has been carried out with a new series of binary catalyst system Nd(OR)_3-mG_m-AlEt₃. The catalytic activity as well as the microstructure of the resulting polymer have been studied. The results indicate that the stereospecificity of the polybutadiene obtained with these binary catalyst system (when m = 2) is similar to that prepared with ternary system Nd(OR)₃-Al₂Et₃Cl₃-AlEt₃, yet the catalytic activity of the former is somewhat higher. Thus possibly, the present simpler binary system is preferable to the ternary system when applied to the polymerization of butadiene.     

COPOLYMERIZATION OF BUTADIENE AND ISOPRENE CATALYZED BY V(acac)_3-Al(i-Bu)_2Cl-Al_2Et_3Cl_3 CATALYST AND CHARACTERIZATION OF THE PRODUCTS

Copolymerization of butadiene and isoprene catalyzed by the catalyst system V(acac)_3-Al(i-Bu)_2Cl-Al_2Et_3Cl_3 has been studied. Composition, microstructure, crystallinity and melting point of the copolymer obtained were determined by PGC, IR, X-ray diffraction and DSC methods respectively. The results revealed that the product was a copolymer and not a blend. The butadiene units presented in the copolymer were of trans-1,4-configuration, while the isoprene units were of both trans-1,4-and 3,4-forms. The melting point and crystallinity of the copolymer decrcascd with increase of molar ratio of isoprene to hutadiene.     

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.     

Initiation and propagation steps in the equibinary polymerization of butadiene by bis(h3-allylnickel trifluoroacetate)

Polymerization of butadiene by bis(h³-allylnickel trifluoroacetate) in benzene and o-dichlorobenzene solvents yields an equibinary 1,4-polybutadiene, containing equal amounts of cis and trans isomers. Initiation proceeds by addition of the allylic moiety of the initiator to a butadiene molecule. The rate of initiation is high enough to ensure complete consumption of the catalyst for a monomer/catalyst molar ratio of about 10 at 5°C. The propagation exhibits the characteristics of a “living” polymerization: the molecular weight is proportional to the conversion, and at the end of the reaction, the average degree of polymerization is equal to the monomer/catalyst molar ratio. Living polybutadienyl-nickel trifluoroacetate is able to reinitiate not only butadiene polymerization but also allene polymerization. However, for high [monomer]/[catalyst] ratios, conversion-dependent transfer reactions limit the molecular weight to 7000 in benzene and to 70,000 in bulk polymerization in the presence of small amounts of o-dichlorobenzene.     

Reaction Mechanism of One-Step Conversion of Ethanol to 1, 3-Butadiene over Zn-Y/BEA and Superior Catalysts Screening

The one-step conversion of ethanol to 1, 3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts. However, the reaction mechanism from ethanol to butadiene is complex and has not yet been fully elucidated, and no catalyst screening effort has been done based on central metal atoms. In this work, density functional theory (DFT) calculations were employed to study the mechanism of one-step conversion of ethanol to butadiene over Zn-Y/BEA catalyst. The results show that ethanol dehydrogenation prefers to proceed on Zn site with a reaction energy of 0.77 eV in the rate-determining step, and the aldol condensation to produce butadiene prefers to proceed on Y site with a reaction energy of 0.69 eV in the rate-determining step. Based on the mechanism revealed, six elements were selected to replace Y for screening superior combination of Zn-M/BEA (M=Sn, Nb, Ta, Hf, Zr, Ti; BEA: beta polymorph A) for this reaction. As a result, Zn-Y/BEA (0.69 eV) is proven to be the most preferring catalyst compared with the other six ones, and Zn-Zr/BEA (0.85 eV), Zn-Ti/BEA (0.87 eV), and Zn-Sn/BEA (0.93 eV) can be potential candidates for the conversion of ethanol to butadiene. This work not only provides mechanistic insights into one-step catalytic conversion of ethanol to butadiene over Zn-Y/BEA catalyst but also offers more promising catalyst candidates for this reaction.     

MoCl_4-(i-Bu)_2AlOAr体系引发丁二烯聚合的研究

由MoCl_4为主催化剂,(i-Bu)_3Al与酚类反应的产物(i-Bu)_2AlOAr为助催化剂所组成的催化体系,在加氢汽油中引发丁二烯聚合,研究酚类结构对聚合反应的影响。结果表明,带有推电子基团的酚类,可以提高丁二烯岵,聚合速度,其顺序为双酚A>间甲酚间>β-萘酚>苯酚>对氯酚。测定了丁二烯聚合的表现活化能E_α,催化剂利用率α,活性中心浓度[P~*],和活性中心的平均寿期(?)。     

Polymerization and copolymerization of 2-phthalimidomethyl 1,3-butadiene. I. Preliminary studies of free radical polymerization and polymerizations initiated by various transition metal allyl complexes

2-Phthalimidomethyl 1,3-butadiene was homopolymerized and copolymerized with butadiene by free radical initiators; r₁ and r₂ were close to 1. All the attempts to polymerize 2PMB anionically have been unsuccessful. Preliminary studies of various η³-allylic catalysts showed that η³-allyl M₀(CO)₃OOCCF₃ initiates the polymerization of butadiene and is not sensitive to N-methyl phthalimide (NMP); neither does it initiate the copolymerization of butadiene and 2PMB. On the other hand, a catalyst that results from the reaction of allyl trifluoroacetate with nickel tetracarbonyl is efficient for the copolymerization of butadiene and 2PMB. η³-Allyl nickel trifluoroacetate was prepared in heptane or benzene and used in benzene or methylene chloride. In all cases it initiated the copolymerization of butadiene with 2PMB     

Electron spin resonance study on polymerization of conjugated dienes by homogeneous catalyst derived from n-butyl titanate and triethylaluminum

Polymerizations of butadiene, penta-1,3-diene, and isoprene with n-butyl titanate–triethylaluminum catalyst are examined by ESR measurements on the polymerization state. At Al/Ti molar ratios greater than 2.9 where the conjugated dienes are polymerized, the polymerization system of butadiene always gives an ESR signal with a g value of 1.983 and with a hyperfine structure of about 19 components. This signal does not appear at all, even in the presence of the monomer, at Al/Ti molar ratios smaller than two where butadiene is not polymerized. The absorption intensity of the signal coincides fairly well with the concentration of polymer chain calculated from polymer yield and the molecular weight. On the basis of these facts, the signal is assigned to the growing end of polybutadiene with this catalyst. The structure of the growing end is proposed to have both two substituted π-allyl groups and an alkoxy group in coordination to titanium (III), by analysis of the hyperfine structure. The polymerization system of penta-1,3-diene and that of isoprene respectively, give a new signal with a g value of 1.983, although the signal for the former monomer has a hyperfine structure of 11 components and that for the latter monomer has no hyperfine structure. A structure for the growing end in the polymerization of each of these two monomers analogous to that of the growing end of polybutadiene is proposed.     

Alternating copolymer of butadiene and propylene. III

Alternating copolymerizations of butadiene with propylene and other olefins were investigated by using VO(acac)₂–Et₃Al–Et₂AlCl system as catalyst. Butadiene–propylene copolymer with high degree of alternation was prepared with a monomer feed ratio (propylene/butadiene) of 4. Alternating copolymers of butadiene and other terminal olefins such as butene-1, pentene-1, dodecene-1, and octadiene-1,7 were also obtained. However, the butadiene–butene-2 copolymerization did not yield an alternating copolymer but a trans-1,4-polybutadiene.     

The characteristics of lanthanide coordination catalysts and the cis-polydienes prepared therewith

The stereoregularity of polydienes is almost the same in regard to the individual elements of the lanthanide series, whereas the activity of the Ln catalysts in diene polymerization varies from one to the other within the series. The latter may be attributed to the difference in the number of electrons that occupy the 4f orbitals. It has been proved that the polymerization of dienes with Ln catalysts under certain conditions proceeds by a “living polymer” mechanism. With regard to the polymerization of butadiene, the most active catalyst is a Nd³⁺species a new binary system of NdCl₃-3ROH + AlR₃ has been discovered. The cis- 1,4 content in polybutadiene is about 97% and the 1,2 content, less than 1%. For the polymerization of isoprene with a Nd³⁺ catalyst system, the effects of ligand and alkyl groups in AIR₃ on cis-1,4 content (ca. 95%) in polyisoprene can be neglected. For the copolymerization of butadiene and isoprene, the cis-1,4 contents of these two monomeric units in the copolymer are greater than 95% the reactivity ratios r₁ and r₂ are determined. and the T_g's of the copolymers of various compositions deviate slightly from the calculated values for random copolymers. A linear relationship exists between the yield strength from the stress-strain curve of Ln-polvbutadiene and its [n] This relationship is verified by Ln-polyisoprene and natural rubber but different slopes are obtained     

在Fe-Zn-Mg催化剂上丁烯-1氧化脱氢制丁二烯动力学

用玻璃流动外循环反应器研究了Fe_4.9Zn_0.9Mg_0.1(原子比)催化剂上丁烯-1氧化脱氢动力学,丁烯-1氧化脱氢制丁二烯、丁烯-1及丁二烯深度氧化生成CO₂的动力学用双反应分子强吸附的L-H(LangmuirHinshelwood)机理方程描述。速度方程的参数用非线性最小二乘法估计,得丁二烯生成速度r_D和CO₂生成速度r_co2的动力学方程式。     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Computational Study of Metathesis Degradation of Rubber, 3. Distribution of Cyclic and Linear Oligomers via Intermolecular Degradation of cis‐Poly(butadiene)

The molecular modeling of the product distributions for the intermolecular metathesis degradation of cis‐poly(butadiene) (cis‐PB) in the presence of ethylene as chain‐transfer agent (CTA) at 298.15 K using the B3LYP/6‐31G (d, p) level of theory reveals that chain–ring and chain‐chain equilibria are shifted toward the formation of 1,5‐hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is negligible. The α,ω‐vinyl‐terminated butadiene oligomers–1,5‐hexadiene equilibrium constant depends on the cis/trans isomer ratio in linear butadiene molecules. While the concentration of 1,5‐hexadiene at equilibrium with cis‐butadiene oligomers is 86 mol‐%, this value for trans‐butadiene oligomers corresponds to 50 mol‐% of 1,5‐hexadiene. The results of calculations are in reasonable agreement with recent experimental data on the intermolecular metathesis of 1,4‐cis‐PB with ethylene using a well‐defined ruthenium alkylidene catalyst. The calculations predict that cis‐butene as a CTA is more efficient in the metathesis depolymerization of cis‐PB compared with ethylene.     

Recycling in telomerization of butadiene with D‐xylose: Pd(TPPTS)n‐KF/Al2O3 as an active catalyst

A palladium‐TPPTS catalyst heterogenized on KF/alumina has been shown to be effective and recyclable for the selective formation of monooctadienylxylopyranosides via the telomerization of butadiene with D ‐xylose. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Nd(OR)3-nCln-AlEt3催化体系对丁二烯的聚合 I.聚合的一般规律

Homopolymerization of butadiene has been carried out with a new series of binary catalyst system Nd(OR)3-nCln-AlEt3 and the catalytic activity as well as the microstructure of the resulting polymer have been studied. The results indicate that the stereospecificity of the polybutadiene obtained with these beinary catalyst system (when n=2) is similar to that prepared with thernary system Nd(OR)3-Al2Et3Cl3-AlEt3, yet the catalytic activity of the former is somewhat higher. Hence, it is possible that the present simpler binary system is more preferable to be applied than the ternary. System in butadiene polymerization.     

The Ti3AlC2 MAX Phase as an Efficient Catalyst for Oxidative Dehydrogenation of n‐Butane

Dehydrogenation or oxidative dehydrogenation (ODH) of alkanes to produce alkenes directly from natural gas/shale gas is gaining in importance. Ti₃AlC₂, a MAX phase, which hitherto had not been used in catalysis, efficiently catalyzes the ODH of n‐butane to butenes and butadiene, which are important intermediates for the synthesis of polymers and other compounds. The catalyst, which combines both metallic and ceramic properties, is stable for at least 30 h on stream, even at low O₂:butane ratios, without suffering from coking. This material has neither lattice oxygens nor noble metals, yet a unique combination of numerous defects and a thin surface Ti_1?yAl_yO_2?y/2 layer that is rich in oxygen vacancies makes it an active catalyst. Given the large number of compositions available, MAX phases may find applications in several heterogeneously catalyzed reactions.     

The nature of active sites in butadiene polymerization catalyzed by organotitanium(III) derivatives

The stereospecificity of benzyl derivatives of trivalent titanium (R_n TiX_3–n, where X = Cl, I, n = 1–3) in butadiene polymerization was studied. It was found that dibenzyltitaniumiodide is an efficient catalyst of the 1,4-cis-polymerization of butadiene and that tribenzyltitanium forms 1,2-units. In both cases all the titanium-benzyl bonds participated in the initiation reaction and the active sites were polymeric analogues of crotyl derivatives of Ti(III); namely, bis-π-oligobutadienyltitaniumiodide and tris-π-oligobutadienyltitanium. These sites are stable at room temperature. The nature of the active sites in the polymerization of butadiene with Ziegler's 1,4-stereo-specific systems Til₄ (or Til₂Cl₂) + AIR₃ are described.     

MgI2-catalyzed halo aldol reaction: a practical approach to (E)-beta-iodovinyl-beta'-hydroxyketones

A novel generation of 1-iodo-3-siloxy-1,3-butadienes has been developed by reacting trimethylsilyl iodide (TMS-I) with alpha, beta-unsaturated ketones in dichloromethane at 0 degrees C without the use of any catalyst. The halo aldol reaction of these butadiene intermediates with aldehydes was efficiently carried out by using magnesium iodide as the catalyst. Twelve beta-iodo-alpha,beta-unsaturated-beta'-hydroxyketones (halo aldols) have been synthesized under the new condition with excellent geometric selectivity and good chemical yields (>80% chemical yields for 11 examples).