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. 相似文献
Polymerization of p‐(dimethylsilyl)phenylacetylene in toluene at 25 and 80°C using RhI(PPh3)3 as the catalyst afforded highly regio‐ and stereoregular poly(dimethylsilylene‐1,4‐phenylenevinylene)s (cis‐ 3 a and trans‐ 3 a ) containing 98% cis‐ and 99% trans‐vinylene moieties, respectively. Similarly, poly(butylmethylsilylene‐1,4‐phenylenevinylene)s ( 3 b with 91% cis‐ and 95% trans‐structures) and poly(diisopropylsilylene‐1,4‐phenylenevinylene) with 95% trans‐structure were synthesized. All polymers were soluble in common organic solvents. The trans‐type polymers showed red shifts and hyperchromic effects in the UV‐visible spectrum. The onset temperature of weight loss (T0) of cis‐ 3 a was much higher than that of trans‐ 3 a . 相似文献
Solvothermal reaction between Cd(NO3)2, 1,4‐phenylenediacetate (1,4‐PDA) and 1,3‐bis(pyridin‐4‐yl)propane (bpp) afforded the title complex, [Cd(C10H8O4)(C13H14N2)]n. Adjacent carboxylate‐bridged CdII ions are related by an inversion centre. The 1,4‐PDA ligands adopt a cis conformation and connect the CdII ions to form a one‐dimensional chain extending along the c axis. These chains are in turn linked into a two‐dimensional network through bpp bridges. The bpp ligands adopt an anti–gauche conformation. From a topological point of view, each bpp ligand and each pair of 1,4‐PDA ligands can be considered as linkers, while the dinuclear CdII unit can be regarded as a 6‐connecting node. Thus, the structure can be simplified to a two‐dimensional 6‐connected network. 相似文献
Thermal properties of cis-1,4-poly(butadiene), Europrene cis, were investigated by means of thermal analysis and complementary methods. Thermal analysis of polymer was carried out both in air and inert atmosphere with a derivatgraph, DSC and internal TG-FTIR coupling system as well as internal TG, DTA-MS coupling system. It was found that investigations in air atmosphere the method of the sample preparation ofcis-1,4-poly(butadiene) influences the results of thermal analysis, which is connected with the rate oxygen diffusion into the reaction zone. Taking into consideration both the method of the sample preparing and atmosphere of thermal studies, the values of activation energy of destruction of cis-1,4-poly(butadiene) were determined. Using TG-FTIR and TG-MS methods, some products of thermal destruction of elastomer were determined.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
The (cis-1,4 and 1,2) polybutadiene polymerized with iron catalyst was investigated by ~(13)C-NMR. Assignments have been made on the spectra for all peaks of the aliphatic and olefinic carbons using chemical shift corrective terms together with Furukawa parameters. The relative intensities of peaks were calculated from the Bernoulli distribution of cis-1,4 and 1,2 units.Quantification of cis-1,4 and 1,2 contents, sequence distribution, alternation pattern of cis-1,4 and 1,2 units, and the chain propagation mechanism were discussed as a result of the detailed study of the spectra. 相似文献
A study was made of the microstructural changes that occur in ultraviolet irradiation under vacuum of thin films of 1,2-poly(cis-1,4-hexadiene) (CHD), 1,2-poly(trans-1,4-hexadiene) (THD), 1,2-poly(trans-1,3-pentadiene) (TPD), equibinary (1,2,-1,4) polybutadiene (EB), and equibinary (3,4-1,4) polyisoprene (EI). These polymers—all containing pendant double bonds—undergo important photoinduced loss of unsaturation, presumably through cyclization of the double bonds, by analogy to the previously reported photocyclization of 1,2-polybutadiene (VB) and 3,4-polyisoprene (VI)films. For the equibinary polymers, which contain internal as well as external (or pendant) double bonds, the loss of unsaturation is considered to involve photocyclization of 1,2-1,4 and 1,2-1,2 dyads in EB and of 3,4-1,4 and 3,4-3,4 dyads in EI. Accompanying thecyclization process in CHD, THD, and TPD is a direct photochemical cis-trans isomerization of ? CH?CH? double bonds analogous to that originally noted for 1,4-polybutadiene. The photorearrangements in the above polymers with pendant double bonds were compared to the corresponding thermally induced rearrangements reported previoulsy;for VB and VI, in particular, the thermal, photo-and radiation-induced cycli-zations were found to be very similar, possibly having a common nonradical, nonionic mechanism involving excited double bonds. 相似文献
Summary: A comparison between the crystal structure of isotactic cis‐1,4‐poly(1,3‐pentadiene) previously predicted by molecular mechanics calculations and that successively determined by other authors by experimental data is reported. The agreement between the two structures is very good as far as the space group, the unit cell parameters and the conformation of the polymer chain are concerned. The mode of packing of the chains proposed in the experimental crystal structure is very similar to that found as relative minimum in the previous energy calculations. The coexistence, in different amounts, of these two modes of packing is suggested by the analysis of the simulated X‐ray spectra and by the results of new energy calculations.
A mode of packing of chains of isotactic cis‐1,4‐poly(1,3‐pentadiene). 相似文献
The title compound, [Cd3(C8H10O4)3(C12H9N3)2(H2O)2]n or [Cd3(chdc)3(4‐PyBIm)2(H2O)2]n, was synthesized hydrothermally from the reaction of Cd(CH3COO)2·2H2O with 2‐(pyridin‐4‐yl)‐1H‐benzimidazole (4‐PyBIm) and cyclohexane‐1,4‐dicarboxylic acid (1,4‐chdcH2). The asymmetric unit consists of one and a half CdII cations, one 4‐PyBIm ligand, one and a half 1,4‐chdc2− ligands and one coordinated water molecule. The central CdII cation, located on an inversion centre, is coordinated by six carboxylate O atoms from six 1,4‐chdc2− ligands to complete an elongated octahedral coordination geometry. The two terminal rotationally symmetric CdII cations each exhibits a distorted pentagonal–bipyramidal geometry, coordinated by one N atom from 4‐PyBIm, five O atoms from three 1,4‐chdc2− ligands and one O atom from an aqua ligand. The 1,4‐chdc2− ligands possess two conformations, i.e.e,e‐trans‐chdc2− and e,a‐cis‐chdc2−. The cis‐1,4‐chdc2− ligands bridge the CdII cations to form a trinuclear {Cd3}‐based chain along the b axis, while the trans‐1,4‐chdc2− ligands further link adjacent one‐dimensional chains to construct an interesting two‐dimensional network. 相似文献
(1RS,3RS,4RS,10SR)‐2,2,3,10‐Tetrabromo‐1,2,3,4‐tetrahydro‐1,4‐ethanonaphthalene, C12H10Br4, (I), is the first structure to be reported with four Br atoms bound to a 1,4‐ethanonaphthalene framework and also the first which possesses three Br atoms in exo positions. Interactions between the Br atoms [three short intramolecular Br...Br distances of 3.1094 (4), 3.2669 (4) and 3.4415 (5) Å] have little effect on the C—C bond lengths but lead to significant twisting of the cage structure compared with the parent hydrocarbon, which is expected to be fully eclipsed at the two saturated C2H4 bridge positions. Chemically related (1SR,4RS)‐2,3‐dibromo‐1,4‐ethenonaphthalene, C12H8Br2, (II), obtained by double dehydrobromination of (I), represents the first structure of any halogen‐substituted benzobarrelene. This cis‐dibromide shows little evidence of steric congestion at the double bond [Br...Br = 3.5276 (8) Å] as a consequence of the large C—C—Br angles [average C=C—Br angle = 126.15 (10)°]. 相似文献
The microstructural changes that occur in cis and trans forms of 1,2-poly(1,4-hexadiene) during methylene blue-photosensitized oxidation were examined by infrared (IR) and 13C-NMR spec-troscopy. The singlet oxygenation of these polymers yielded the expected allylic hydroperoxides accompanied by double bond shifts to new vinyl and trans-vinylene double bonds. The photosensitized oxidation exhibited zero-order kinetics; the relative rates for the cis- and trans-1,2-poly(1,4-hexadiene)s were approximately 3.8:1.0. 相似文献
In the 1H-NMR spectrum of polychloroprene dissolved in C6D6, the ?CH proton signal was separated into two triplet peaks. These triplet signals were assigned to the ?CH proton in the trans-1,4 and cis-1,4 isomers by measurement of 1H-NMR spectra of 3-chloro-1-butene and a mixture of trans- and cis-2-chloro-2-butene as model compounds for the 1,2, trans-1,4 and cis-1,4 isomers. In 1H-NMR spectra (220 Mcps) of polychloroprene dissolved in C6D6, two triplet signals were separated completely from which the relative concentrations of trans-1,4 and cis-1,4 isomers could be obtained quantitatively. 相似文献
The crystal structure of the title compound, C20H23N3O7, consists of relatively isolated molecules. The substituted 1,4‐dihydropyridine ring adopts a flattened boat conformation. Both ester groups, at positions 3 and 5, have cis,cis geometry. The phenyl ring is nearly planar and is approximately perpendicular to the 1,4‐dihydropyridine ring (dihedral angle 87.70°). 相似文献
Stress, strain, and birefringence measurements have been carried out on swollen and unswollen networks of ′cis-1,4-polybutadiene polymers. Neither stress-strain nor birefringence-strain relations of unswollen specimens obey the Gaussian network theory, but both can be fitted by the Mooney-Rivlin equation. On the contrary, data on specimens swollen in tetralin, decalin, benzene, and carbon tetrachloride strictly obey the Gaussian network theory. Existing methods for evaluating the temperature coefficient of the unperturbed dimensions, d In 〈r2〉/dT, from the stress-temperature relation are applied to the present data and discussed in some detail. It is concluded that reliable values of d In 〈r2〉/dT are not obtainable from data on unswollen samples because of the pronounced non-Gaussian effect. The value 7.5 Å3 for the optical anisotropy Å3 (an alternative to the stress-optical coefficient) for unswollen specimens is markedly larger than values (5.8 Å3 on the average) for swollen specimens. This is interpreted as due to the shortrange orientational order among polymer segments. The quantities 〈r2〉, ΔΓ, and their temperature coefficients are calculated for both cis-1,4-polybutadiene and cis-1,4-polyisoprene chains, on the basis of the rotational isomeric state approximation for bond rotations. Values of ΔΓ for cis-1,4-polybutadiene calculated using Clément and Bothorel's set of anisotropic bond polarizabilities are in good agreement with observed values for swollen specimens. Those for cis-1,4-polyisoprene obtained using the same set of anisotropic bond polarizabilities are somewhat smaller than observed values for unswollen specimens. This departure is in the direction expected from the behavior of ΔΓ upon swelling (i.e., a decrease in ΔΓ upon swelling). 相似文献
Several typical 13C‐NMR displacements (of C?O, C(α), C(β), and Cipso), as well as conformational or energy properties (S? N? C?O dihedral angle, ΔE syn/anti; HOMO/LUMO) could be correlated with the electronic parameters of p‐substituted N‐cinnamoylbornane‐10,2‐sultams 2 . Even under nonchelating conditions, the pyramidalization of the sultam N‐atom decreases for electron‐attracting p‐substituents, inducing a modification of the sultam‐ring puckering. Detailed comparison of the X‐ray structure analyses of 2b, 2d , and 2m showed that the orientation of the sterically directing pseudo‐axial S?O(2) and H? C(2) is modified and precludes any conclusion about the π‐facial stereoelectronic influence of the N lone pair on the alkyl Grignard 1,4‐addition. We also showed that the aggregating alkyl Grignard reagent may be used in equimolar fashion, demonstrating that the sultam moiety is chelated with a Lewis acid such as MgBr2. The Schlenk equilibrium may also be used to generate the appropriate conditions of effective 1,4‐diastereoselectivity. Although the anti‐s‐cis/syn‐s‐cis difference of conformational energies for N‐cinnamoyl derivatives 2 is higher than for the simple N‐crotonoyl analogue, an X‐ray structure analysis of the SO2/C?O syn derivative 10 confirms the predictive validity of our conformational calculations for ΔE≤1.8 kcal/mol. 相似文献