Electron spin resonance study of polymerization of butadiene with tris(acetylacetonato)titanium and triethylaluminum

ESR spectra of homogeneous catalyst derived from tris(acetylacetonato)titanium(III) and triethylaluminum were observed at several temperatures from ?78°C, to +25°C, at molar ratios of aluminum to titanium of 1–108. At ?78°C, this catalyst yields a violet complex which shows an ESR signal with a g value of 1.959 and is associated with the first intermediate. At ?40°C to ?30°C, this signal decreases, and two signals with g values of 1.947 and 1.960 are observed. The latter two signals diminish at ?5°C to +10°C, while two kinds of new signals with g values of 1.965 and 1.969 appear overlapping each other. The structures of the species corresponding to these five signals are discussed on the basis of the ESR spectra, the intensity change, and the unpaired spin distribution. A new signal with a g value of 1.978 is found in the presence of butadiene at 25°C at Al/Ti > 8 and is assigned to a growing end of polybutadiene with this catalyst. The polymer yield increases remarkedly at Al/Ti molar ratios greater than 10. The microstructure of the resulting polymer consists almost completely of 1,2 units. The structure of the growing end is proposed to be a titanium (III) species containing two 1-substituted allyl groups, by comparison with the structure ascribed to the growing end of polybutadiene with n-butyl titanate-triethylaluminum catalyst.     

Electron spin resonance study on homogeneous catalysts derived from n-butyl titanate and triethylaluminum

ESR spectra of homogeneous catalyst systems derived from n-butyl titanate and triethylaluminum at Al/Ti molar ratios of 1.0–10 were observed in toluene solution at several temperatures from ?78°C to +25°C. In the whole range of Al/Ti molar ratios, a single signal with a g value of 1.951 was observed at ?78°C and was associated with the first reaction intermediate. With increasing temperature, the intensity of the signal decreased gradually, while two series of signals appeared, depending on the Al/Ti molar ratio. At an Al/Ti molar ratio of 1.7, seven kinds of signals with g values of 1.960, 1.946, 1.950, 1.959, 1.980, 1.977, and 1.978, respectively, were observed. On the other hand, four kinds of signals with g values of 1.934, 1.966, 1.952, and 1.979, respectively, were found at Al/Ti molar ratios larger than 3. The structures of the species corresponding to the signals were discussed on the basis of the ESR spectra, the order of their growth and their hyperfine structures being considered. Two series of ESR signal were correlated to two kinds of active species for polymerization of styrene and butadiene, respectively.     

Electron spin resonance study on polymerization of alkyl acrylates with n-butyl titanate(IV)–triethylaluminum catalyst

n-Butyl titanate(IV)–triethylaluminum catalyst at Al/Ti molar ratios greater than 6 polymerizes methyl and n-butyl acrylates at ?78°C. The polymerization system which includes methyl acrylate at ?78°C, gives two ESR signals with g factors of 1.958 and 1.961 that overlap each other. The absorption intensity of the latter signal is approximately proportional to the polymer chain concentration calculated from polymer yield and the molecular weight. The polymerization system at Al/Ti ratios smaller than 3 has no catalytic activity on the polymerization and shows only the ESR signal with the g factor of 1.958. On the basis of these facts the ESR signal with the g factor of 1.961 is attributed to the active growing end of poly(methyl acrylate) with this catalyst. The character of this active growing end is discussed.     

Two-step regioselective synthesis of 1,2-difluorobenzenes from chlorotrifluoroethylene and buta-l,3-dienes

Russian Chemical Bulletin - The gas-phase copyrolysis of chlorotrifluoroethylene with buta-1,3-diene, penta-1,3-diene, or isoprene in a flow reactor at 440–480°C gave...     

Reactions Between AIRCl2 and Ti (OR)4 and Activity in Diolefin Polymerization

Through the use of a Ti(OR′)₄-AlRCl₂ catalyst system, high 1,4-cis isoprene polymers and crystalline 1,4-trans polybutadiene are obtained. Neither monomer is polymerized at a Al/Ti mole ratio of less than 4. The maximum activity and stereospecificity for isoprene is observed at Al/Ti = 4. For 1,4-trans butadiene polymers the activity increases progressively with increasing Al/Ti ratio. The investigations carried out on this catalyst system show that at a AI/Ti mole ratio of 4 the formation of crystalline β-TiCl₃ takes place, while at lower ratios insoluble chloro-alkoxide derivatives of Ti^III with different compositions separate. Soluble complexes containing aluminium and titanium are initially formed before precipitation occurs. Chemical data and investigations by IR and NMR spectroscopy indicate exchange reactions between Al-Cl, Al-R, and Ti-OR groups, together with reduction of the transition metal. A reaction mechanism and a hypothesis on the nature of the active catalyst are given.     

Inclusion polymerization in perhydrotriphenylene studied by ESR spectroscopy: Growing chain structure and conformation of methylsubstituted polybutadienes

Inclusion polymerization of diene monomers promoted by γ rays and performed in perhydrotriphenylene was studied by ESR techniques. During polymerization of butadiene, 1,3-pentadiene, isoprene, 2,3-dimethylbutadiene, 2-methylpentadiene, and 2,4-hexadiene, spectra attributable to allyl-type radicals were collected. It was demonstrated they actually represent the propagating radicals and they do not vary over a long period of time. They are not temperature dependent in the range ?150°/ +60°C, apart from the radical of polybutadiene, suggesting that the included methyl-substituted polybutadienes are conformationally fixed. When the two opposite insertions of monomers 1,4 and 4,1 are distinguishable, the radicals bearing the higher number of methyl groups at the ends of allyl system prevail.     

Copolymerisation du trans-pentadiene-1,3 et de l'isoprene amorcee par le systeme triethylaluminium-orthotitanate de n-butyle

L'isoprene and 1,3-pentadiene can be polymerized in benzene solution with the use of a catalyst prepared from triethylaluminium and n-butyl orthotitanate. The structures of these copolymers are independent of Al/Ti molar ratio. There are more vinylic units in the copolymer than in the homopolymers. The determination of the monomer reactivity ratios, ozonolysis and pyrolysis show that copolymers are predominantly statistic with a slight tendency towards alternation.     

Copolymerization of 1,3‐butadiene and isoprene with cobalt dichloride/methylaluminoxane in the presence of triphenylphosphine

The homopolymerization and copolymerization of 1,3‐butadiene and isoprene were achieved at 0 °C with cobalt dichloride in combination with methylaluminoxane and triphenylphosphine (Ph₃P). For 1,3‐butadiene, highly cis‐specific and 1,2‐syndiospecific polymerization proceeded in the absence or presence of Ph₃P, respectively, although the activity with Ph₃P was much higher than that without Ph₃P. Only a trace of the polymer was, however, obtained in isoprene polymerization when Ph₃P had been added. For copolymerization, the polymer yield in the presence of Ph₃P was about three times higher than that in its absence. Copolymerization in the presence of Ph₃P was, therefore, investigated in more detail. Unimodal gel permeation chromatography elution curves with narrower polydispersity (weight‐average molecular weight/number‐average molecular weight ≈ 1.5) indicated that the propagation reaction proceeded by single‐site active species. Both the yield and molecular weight of the copolymer decreased with an increasing amount of isoprene in the feed, and this was followed by an increase in the isoprene content in the copolymer. The monomer reactivity ratios, r₁ (1,3‐butadiene) and r₂ (isoprene), were estimated to be 2.8 and 0.15, respectively. Although the 1,3‐butadiene content in the copolymer was strongly dependent on the comonomer composition in the feed, the ratio of 1,2‐inserted units to 1,4‐inserted units of 1,3‐butadiene was constant. Concerning the isoprene unit, the percentage of 1,2‐ and 3,4‐inserted units was increased at the expense of 1,4‐inserted units with an increasing isoprene content in the feed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3086–3092, 2002     

Cyclo- and cyclized diene polymers. XIII. γ-Ray-initiated polymerization of 1,3-dienes

The γ-ray-initiated polymerization of butadiene, isoprene, and 2,3-dimethylbutadiene-1,3 was carried out at temperatures of 20°C. and ?78°C. Polymers of butadiene and isoprene with mixed linear and cyclic structure were proved to result from the polymerization at ?78°C. A monocyclic structure was found for the 2,3-dimethylbutadiene-1,3 polymers initiated either at ?78°C. or in the thiourea canal complex at 20°C.     

Diels–Alder reactions of perfluoroketene dithioacetals with electron-rich 1,3-dienes: a new access to polysubstituted aromatic sulfides

The present paper describes the Diels–Alder reactions of perfluoroketene dithioacetals with electron-rich 1,3-dienes (2,3-dimethylbuta-1,3-diene, isoprene, penta-1,3-diene) followed by spontaneous HF and thiol elimination, leading to polysubstituted aromatic sulfides in moderate to good yields. Reactions seem to be dependent on the substitution patterns of perfluoroketene dithioacetals; the best results were obtained from trifluoromethyl or pentafluoroethyl and ethylsulfanyl derivatives. Theoretical calculations performed at the DFT level are in good agreement with the experimental results and show that the overall process is controlled by the cycloaddition step.     

Mechanism of stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts. I. Effects of the species of transition metals

Butadiene was polymerized by catalysts of the type: metal acetylacetonate (metal: Ti to Ni in the periodic table)–triethylaluminum–aluminum halide, with various ratios of triethylaluminum to aluminum halide. The minimum cis content was observed with vanadium catalyst in all cases, while the minimum polymer yields were observed with the iron and the manganese catalysts. These transition metal effects are discussed in terms of the crystal field theory, and it is suggested that the electrostatic interaction between the nearly nonbonding electrons of transition metal atom and a butadiene molecule or a growing end of the polymeric chain plays an important role in the stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts.     

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.     

Diethylbis(2,2′‐bipyridine)iron/MAO. A Very Active and Stereospecific Catalyst for 1,3‐Diene Polymerization

Diethylbis(2,2′‐bipyridine)Fe/MAO is an extremely active catalyst for the polymerization of 1,3‐dienes. Polymers with a 1,2 or 3,4 structure are formed from butadiene, isoprene, (E)‐1,3‐pentadiene and 3‐methyl‐1,3‐pentadiene, while cis‐1,4 polymers are derived from 2,3‐dimethyl‐1,3‐butadiene. The 1,2 (3,4) polymers obtained at 25°C are amorphous, while those obtained below 0°C are crystalline, as was determined by means of X‐ray diffraction. Mechanistic implications of the results are briefly discussed.     

丁二烯－甲基丙烯酸甲酯嵌段共聚物的阴离子聚合及表征

讨论了用阴离子方法进行了二烯与甲基丙烯酸甲酯共聚合的过程，并用ＧＰＣ、ＦＴＩＲ、ＮＭＲ和动态粘弹谱对共聚物进行了表征．证明所得聚合物为具有较高分子量、窄分布的二嵌段共聚物．     

Polymérisation anionique amorcée par les composés lamellaires du graphite et du lithium

In the present work, we use the binary insertion compound LiC₁₂ to polymerize styrene, methyl methacrylate, butadiene, isoprene, and to copolymerize isoprene and styrene in various hydrocarbon solvents (aromatics and aliphatic) and etheral solvents. We show that the styrene polymerization in aromatic solvents gives better yields than in the etheral solvents, the polymer being atactic. Methyl methacrylate does not polymerize in toluene but does so completely in DME. More generally, the yields of polymerization are better with KC₃₇ than with LiC₁₂ because of the different capacities of the monomer to get into the carbon layers. The polymerization of dienes with LiC₁₂ shows that the microstructures of the polymer obtained in π-or n-donor solvents are similar to the ones obtained by homogenous polymerization with Li cation in such solvents. However, for isoprene in cyclohexane, the results are different. The isoprene styrene copolymers are statistical ones and the mean length of styrene blocks is less than 5. The monomer interaction with the insertion compound and the growing chain geometry between the carbon layers are the facts which control either the stereospecificity of the polymerization or the selectivity of the copolymerization.     

Use of Cryptates om Bulk Anionic Polymerization of Dienes

The bulk polymerization of isoprene and butadiene with organoalkati compounds in the presence of cryptants has been studied. The effects of monomer concentration, cryptant concentration and counterions on the inductioin period and molecular weight with these same monomers has also been studied. The microstructure of polymers has been determined by ¹H-NMR measurements. In the presence of complexed ion pairs the structure is independent of the temperature, of the initiator concentration, of the counterions, and of the organoalkali/cryptant molar ratio, but the vinyl structure increases with t he cryptant concentrtion.     

Chemo‐ and stereoselective polymerization of 3‐methylenehepta‐1,6‐Diene and Its thiol‐ene modification

Here we report on the coordination polymerization of a vinyl‐functionalized butadiene monomer, 3‐methylenehepta‐1,6‐diene (MHD) with exclusive conjugated diene chemoselectivity, high 1,2‐regioselectivity and moderate isotacticity (1,2‐selectivity > 99%, mm triad = 93%). Random copolymers of MHD and other conjugated diene (isoprene or myrcene) are also synthesized. The pendent vinyl groups of MHD homo or copolymers could be quantitatively converted into various functional groups via thiol‐ene click reaction. The resulting functionalized polybutadiene‐based material display versatile thermal and surface properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1031–1039     

Photoinitiated polymerization of methacrylic monomers in a poly(methyl methacrylate) matrix: A comparative study with other matrices (styrene–butadiene–styrene,polystyrene, and polybutadiene)

The kinetics and mechanism of the photoinitiated polymerization of 1,6‐hexanediol dimethacrylate (HDDMA) in a poly(methyl methacrylate) (PMMA) matrix were studied. The maximum double‐bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination were calculated. For this system, a reaction‐diffusion termination mechanism occurred from the start of the polymerization, and it was predominantly maintained until high monomer concentrations, probably because of the relatively high intermolecular attraction force between the PMMA matrix and HDDMA monomer. In addition, a comparative study of the photoinitiated polymerization of methacrylic monomers in four different polymeric matrices [styrene–butadiene–styrene (SBS), polystyrene (PS), polybutadiene (PB), and PMMA] was carried out. The aggregation state, vitreous or rubbery, of the monomer–matrix system and the intermolecular strength of attraction in the monomer–matrix system and growing macroradical and matrix systems were the principal factors influencing the kinetic and mechanistic behavior of these systems. When PB and SBS were used as matrices, crosslinked polymerized products were obtained as a result of the participation of double bonds of the matrix in the polymerization process (copolymerization). PS sequences in the SBS and PS matrices also took part in the polymerization process through the coupling of the benzylic radical to the growing macroradical. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 120–127, 2002     

Controlled/living radical polymerization of isoprene and butadiene in emulsion

A process for RAFT-controlled radical polymerization in emulsion [36] has been applied to the polymerizations of isoprene and of butadiene in emulsion systems, with the goal of producing latex particles containing block copolymers of acrylic acid (stabilizer and starting polymer), styrene (second polymer) and isoprene or butadiene (third polymer). The microstructure of the polymer chains was examined using dual-detection size-exclusion chromatography, and the nanostructure of the materials was investigated by differential scanning calorimetry and solid-state nuclear magnetic resonance. Reactions were always slow (although faster than the corresponding processes in solution), and exhibited limited reinitiation by isoprene when in emulsion. The materials containing isoprene exhibit a nanostructure with a phase separation into high-T_g polystyrene-rich domains and low-T_g polyisoprene-rich domains, revealed by DSC and NMR. This has the potential to lead to barrier materials with novel physical properties.     

2-alkyl-1,3-butadiene polymerization under the influence of π-allylic complexes of transition metals

Stereoregulation in the polymerization of 2-alkyl-1,3-butadienes with transition metal π-allylic complexes has been studied. The direction of isoprene polymerization is shown to be a function of the nature of the metal and ligands in the allylic compound. The presence of acidic ligands in π-allylic complexes of Zr, Cr, Mo, and Co contributes to 1,4-addition and increases the selectivity of π-allylic nickel complexes, favoring cis-1,4-structure formation. Investigation of the model reaction of 2-alkyl-1,3-butadienes with bis(π-perdeuterocrotyl nickel iodide) revealed that active sites have an π-allylic type structure. The mechanism of formation of π-allylic adducts and the main factors which determine the dependence of direction and rate of polymerization on the nature of a monomer in the diene series: 2-methyl-1,3-butadiene(isoprene), 2-ethyl-1,3-butadiene, 2-isopropyl-1,3-butadiene, and 2-tert-butyl-1,3-butadiene, are discussed.