The barium salt of the dimeric dianion of 1,1-diphenylethylene (Ba-DPhE) initiates polymerization and copolymerization of monomers capable of anionic polymerization (butadiene, isoprene, styrene) in ethereal and hydrocarbon solvents. Ba-DPhE is more stereospecific in butadiene polymerization (up to 70% of cis-1, 4-units in hydrocarbon medium) than initiators based on other metals of Groups I and II. The relative reactivity of monomers in copolymerization processes in THF decreases in an order typical for anionic polymerization: styrene > butadiene > isoprene. The most interesting feature of organobarium initiators is their ability to form random butadiene-styrene copolymers with high cis-1,4-butadiene unit content when copolymerization proceeds in a hydrocarbon medium. A new phenomenon in anionic polymerization, the dependence of diene units structure on copolymer composition, was observed. Thus an increase of styrene content in butadienestyrene copolymer leads to conversion of cis-1,4-butadiene units into trans-1,4-units (in benzene) or to conversion of 1,4-units to 1,2-units (in THF). Similarly, an increase of butadiene content in its copolymer with isoprene (in benzene) leads to conversion of cis-1,4-isoprene units into trans-1,4-units. Spectrophotometric, conductometric, and viscometric methods were used to study organobarium active centers. Certain anomalies connected with the formation of specific aggregates due to coupling of bifunctional hydrocarbon chains with bivalent counterions were observed. 相似文献
The polymerization and catalytic behavior of catalyst systems composed of polymer-supported rare-earth metals were investigated. The catalyst systems show high catalytic activity and stereospecificity for butadiene polymerization. The catalytic efficiency for SMC (styrene-2-(methylsul-finyl)ethyl methacrylate copolymer).NdCl3-Al(i-C4H9)3 system is twice or three times that of the NdCl3.4DMSO system. The activity of the ternary system SAAC (styrene-acrylic acid copolymer).Nd-Ph3CCl-Al(i-C4H9)3 was up to 170 kg polybutadiene/(g Nd-h). The cis-1,4 content of polybutadiene was more than 98%. This system was also used for isoprene polymerization. The cis-1,4 content of the polyisoprene obtained was about 96% 相似文献
Summary: The bis(imino)pyridyl vanadium(III ) complex [VCl3{2,6‐bis[(2,6‐iPr2C6H3)NC(Me)]2(C5H3N)}] activated with different aluminium cocatalysts (AlEt2Cl, Al2Et3Cl3, MAO) promotes chemoselective 1,4‐polymerization of butadiene with activity values higher than classical vanadium‐chloride‐based catalysts. The polymer structure depends on the nature of the cocatalyst employed. The MAO‐activated complex was also found to be active in ethylene‐butadiene copolymerization, producing copolymers with up to 45 mol‐% of trans‐1,4‐butadiene. Crystalline polyethylene and trans‐1,4‐poly(butadiene) segments were detected in these copolymers by DSC and 13C NMR spectroscopy.
A novel linked‐half‐sandwich lutetium–bis(allyl) complex [(C5Me4? C5H4N)Lu(η3‐C3H5)2] ( 1 ) attached by a pyridyl‐functionalized cyclopentadienyl ligand was synthesized and fully characterized. Complex 1 in combination with [Ph3C][B(C6F5)4] exhibited unprecedented dual catalysis with outstanding activities in highly syndiotactic (rrrr>99 %) styrene polymerization and distinguished cis‐1,4‐selective (99 %) butadiene polymerization, respectively. Strikingly, this catalyst system exhibited remarkable activity (396 kg copolymer (molLu h)?1) for the copolymerization of butadiene and styrene. Irrespective of whether the monomers were fed in concurrent mode or sequential addition of butadiene followed by styrene, diblock copolymers were obtained exclusively, which was confirmed by a kinetics investigation of monomer conversion of copolymerization with time. In the copolymers, the styrene incorporation rate varied from 4.7 to 85.4 mol %, whereas the polybutadiene (PBD) block was highly cis‐1,4‐regulated (95 %) and the polystyrene segment remained purely syndiotactic (rrrr>99 %). Correspondingly, the copolymers exhibited glass transition temperatures (Tg) around ?107 °C and melting points (Tm) around 268 °C; typical values for diblock microstructures. Such copolymers cannot be accessed by any other methods known to date. X‐ray powder diffraction analysis of these diblock copolymers showed that the crystallizable syndiotactic polystyrene (syn‐PS) block was in the toluene δ clathrate form. The AFM micrographs of diblock copolymer showed a remarkable phase‐separation morphology of the cis‐1,4‐PBD block and syn‐PS block. This represents the first example of a lutetium‐based catalyst showing both high activity and selectivity for the (co)polymerization of styrene and butadiene. 相似文献
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 相似文献
The polymerization of isoprene with catalytic systems efficient for the cis polymerization of butadiene, i.e., cobalt 2-ethyl hexanoate-diethylaluminum chloride and cobalt 2-ethyl hexanoate-ethylaluminum sesquichloride, is studied. The catalysts are obtained via in situ mixing of the components or at a reduced temperature (0–5°C) in the presence of a small amount of the monomer. In situ polymerization proceeds with an induction period, whose duration depends on the polymerization conditions, or without this period if a preformed catalyst is used. In each case, the resulting polymer is characterized by a mixed microstructure with a predominant content of cis-1,4 units and 3,4 units. 相似文献
A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al(iBu)3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tüds(K-T) method and the Mao-Huglin(M-H) method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers' composition distribution. 相似文献
Titanium complexes were prepared by the reaction of 2,2′-thiobis(6-tert-butyl-4-methylphenol) (TBP) with TiCl4 or Ti(OPri)4. These complexes in combination with methyalumoxane as cocatalyst are highly active towards ethylene and propene, giving polymers having high molecular weights. The polymerization activities for ethylene and propene are comparable to those of Cp2ZrCl2-MAO catalyst. Polypropylene obtained had extremely high molecular weight (Mw>6 million) and low regioregularity (30% of head-to-head and tail-to-tail linkages). Highly syndiotactic polystyrene was obtained with these catalysts with activity up to 27 kg polymer per g Ti and hour. Copolymerization of styrene with ethylene gave highly alternating copolymer with isotactic styrene units. These catalysts are also active toward both conjugated and nonconjugated dienes such as butadiene and 1,5-hexadiene. Polybutadiene had mainly cis-1,4-structure (98%). The structure of poly(1,5-hexadiene) is rather complicated, which is quite different from that prepared with heterogeneous TiCl3 catalysts. 相似文献
The copolymerization of isoprene, butadiene, and other conjugated dienes with maleic anhydride was readily initiated in polar solvents by conventional free radical catalysts, including peroxides, hydroperoxides, and azobisisobutyronitrile, at high concentrations or at temperatures at which the catalyst had a half-life of 1 hr or less and the total reaction time was 0.5-1 hr. Decreasing the reaction temperature or the rate of catalyst addition resulted in increased yields of Diels-Alder adduct and decreased yields of copolymer. The molecular weight decreased as the temperature increased. Dioxane and tetrahydrofuran peroxides, obtained by the passage of oxygen or UV irradiation in air, also initiated the copolymerization. The soluble diene-maleic anhydride copolymers were equimolar and alternating, had [n] 0.1-6 (cyclohexanone) and contained 75-95% 1,4 structure according to ozonolysis, titration with IC1 and NMR. The IR spectrum of the butadiene–maleic anhydride copolymer indicated 75-95% cis-1,4, 5-20% trans-1,4 and 0-5% 1,2-vinyl unsaturation. The proposed mechanism of polymerization involves a donor-acceptor (diene-dienophile) interaction generating a ground-state charge transfer complex which is readily converted to the cyclic adduct. Under the influence of radicals the ground-state complex is transformed into an excited complex which undergoes polymerization. High concentrations of radicals are necessary to generate polymerizable excited complexes in competition with adduct formation. 相似文献
MAO/CpTiCl3 is an active catalyst for the polymerization of various types of 1,3-dienes. Butadiene, (E) - and (Z) −1,3-pentadiene, (E) −2-methyl-1,3-pentadiene and 2,3-dimethylbutadiene yield, at room temperature, polymers with a cis-1,4 or a mixed cis/1,2 structure. 4-Methyl-1,3-pentadiene and (E,E) −2,4-hexadiene give, respectively, a 1,2 syndiotactic and a trans-1,4/1,2 polymer. MAO/CpTiCl2·2THF and MAO/(CpTiCl2)n are less active than the CpTiCl3 catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)-1,3-pentadiene: a cis-1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis-η4 at +20°C and may be trans-η2 at −20°C. Results obtained with catalysts from CpTi(OBu)3 and Ti(OBu)4 are reported for comparison. An interpretation is given of the formation of cis-1,4 isotactic poly(2-methylpentadiene) and of 1,2 syndiotactic poly(4-methylpentadiene), as well as of syndiotactic polystyrene. 相似文献