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951.
The influence of catalysis on chemical modification of 1,2-polybutadienes (Mn < 10,000) by CX3Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl3POCl2) and ethyl trichloroacetate (CCl3CO2Et) in the presence of solvents such as C6H6, CH2Cl2. Among the compounds tested as catalysts for the addition of CX3Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl2, FeCl3, RuCl3 3H2O, Fe2(CO)9 and Cl2Ru(PPh3)3 were found to show high catalytic activity. The most active is Cl2Ru(PPh3)3: used without or with cocatalysts (Et3NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX3Z. The activity of the other catalysts is generally dependent on CX3Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found. 相似文献
952.
V W Burse D F Groce M P Korver P C McClure S L Head L L Needham C R Lapeza A L Smrek 《The Analyst》1990,115(3):243-251
Serum for reference pools of in vivo polychlorinated biphenyls (PCBs) was obtained from four goats that had received one dose (100 mg kg-1) of a selected technical Aroclor (AR) (1016, 1242, 1254 or 1260) and were allowed to recover for 30 d. These pools were used to assess the differences in an analytical method that determines and quantifies PCBs using packed-column gas chromatography (PCGC) (quantified on the basis of mean mass percent. data for grouped PCB peaks) and capillary-column gas chromatography (CCGC) (quantified on the basis of percent. composition data for specific congeners). With CCGC, results were statistically significantly different (p less than or equal to 0.0002) from results with PCGC for ARs 1016, 1242 and 1254 but not for AR 1260 (p = 0.23). When comparing these gas chromatographic methods using bovine serum spiked in vitro with the same ARs at 17-25 p.p.b., it was found that the methods were not statistically significantly different for any of the ARs (p = 0.30-0.92). Levels of serum PCB determined by the two methods for 12 persons, divided into two groups according to exposure, were compared using the paired t-test. Group 1 consisted of three persons with dietary and/or environmental exposure; one with dietary and/or environmental exposure in addition to occupational exposure dating back 20 years. Group 2 consisted of eight persons with recent occupational exposure.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
953.
A sensitive spectrophotometric method based on the extraction of a uranium-benzoate-Malachite Green complex by chlorobenzene is described. The absorption maximum is at 635 nm and the molar absorptivity is 8.3 x 10(4) 1 mole(-1), cm(-1). A preliminary separation of uranium by extraction with methyl isobutyl ketone from acid-deficient aluminium nitrate solution is used to avoid interferences. An aliquot of the extract is then diluted with chlorobenzene and shaken with benzoate buffer containing Malachite Green (MG). The method has been applied for the determination of uranium in a synthetic leach solution. The complex extracted is probably [MG(2)(C(6)H(5)COO)(3)][MG(+)]. 相似文献
954.
The molecular structure of TTF dissolved in nematic liquid crystalline solvents has been determined from the proton magnetic resonance including couplings due to 13C in natural abundance. The molecule is puckered in a boat conformation with the SCHCHS planes making a dihedral angle of 13 ± 2° with the S2C CS2 plane. The other structural parameters obtained are rCH = 1.085 ± 0.014 Å and the angel CCH = 123.7 ± 1.5°. 相似文献
955.
Luminescence of Eu2+ Ions in Fluosilicates MSiF6 (M = Sr, Ba) A pure f → f emission is detected in Eu2+ doped SrSiF6 and BaSiF6. Because of the strong ionic bonding of europium a large gap occurs between the bottom of the 5d band and the 6P7/2 emission level (3000 cm?1 at 300 K). The emission is very intense under low pressure mercury excitation and decreases slowly with temperature. 相似文献
956.
A kinetic study of the aqueous persulphate initiated polymerisation of methacrylamide has shown that the rate of polymerisation is represented by the equation where the overall rate constant, . Chain transfer with monomer, where CM = 5.4 × 10?3 at 60°, is shown to be the dominant transfer step. Comparison with kinetic studies of the analogous acrylamide polymerisation shed doubt on the ‘cage effect’ interpretation of complex orders with respect to monomer. An alternative explanation is proposed. 相似文献
957.
The activation of18O and19F by the reactions18O(γ, p)17N and19F(γ, 2p)17N was determined as a function of the maximum energy of the bremsstrahlung beam. By the use of this method it is possible
to measure oxygen or fluorine by counting the delayed neutrons emitted by17N with a half-life of 4.2 sec.
相似文献
958.
F. Ciardelli O. Pieroni C. Carlini C. Menicagli 《Journal of polymer science. Part A, Polymer chemistry》1972,10(3):809-822
The synthesis of optically active p-sec-butylstyrene (I) has been carried out starting with (S)-2-phenylbutane (II) having optical purity 88–91%. The optical purity of I thus obtained was found to be 73–75%. The polymerization of I with stereospecific coordinated anionic catalysts gave amorphous polymers, as in the case of many other p-substituted styrene derivatives. The fractions obtained from these polymers have very similar rotatory power at 589 nm which is practically equal to that of polymer of I obtained by nonstereospecific radical initiator and of low molecular weight structural models. Accordingly the 1Lb electronic transition of the aromatic chromophore shows a very low rotatory strength in all samples examined. This result is related to the lack in solution of conformations with a predominant single chirality of the main chain of the macromolecules derived from I. 相似文献
959.
E Pfenninger D E Poel C Berse H Wehrli K Schaffner O Jeger 《Helvetica chimica acta》1968,51(4):772-803
Irradiation of 3,19-dioxo-17β-acetoxy-Δ4-androstene ( 2 ) at room temperature in either of its two absorption bands centered at about 245 and 315 nm, respectively, led to products 21, 22 , and 23 (Chart 3). Compounds 21 and 22 result from rearrangements involving intramolecular formal 1,2- (→ 21 ) and 1,3-shifts (→ 22 ) of the angular formyl group, and the formation of compound 23 proceeds through the elimination of the formyl radical and the incorporation of a hydrogen from the medium. Evidence favors the latter process to be a secondary radical reaction rather than a primary photochemical step. 相似文献
960.
The solubility products for some rare earth hydroxides and their temperature dependence have been shown. Greater solubility is shown for larger atomic radii and for lower temperature. 相似文献