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51.
It is shown that in thermal polymerization of styrene four dimers and six trimers are formed by parallel occurring oligomerization reactions. With increasing temperature the rate of oligomerization increases more rapidly than the rate of polymerization. The relativ yields of the different oligomers depend on temperature, too. 相似文献
52.
The technological properties of ABS polymers largely depend on the structure of the elastomer phase as well as on the elastomer/thermoplast interface. The morphological structure of such polymers can be determined from electron micrographs of ultramicrotome sections – after selective contrasting of the polybutadiene phase – or of replicas of fracture surfaces after selective chemical degradation. The various ABS polymers are classified by their manufacturing processes and their morphologies and characterized by electron micrographs. The degree and place of grafting are of particular importance. The quantitative determination of the surface- and internal grafting is achieved by combining the determination of the degree of grafting (extraction), the evaluation of the results obtained on particle counting, and a morphometric process. It is demonstrated that the morphometric process can in general be applied for the quantitative determination of the contrastable component in two-phase polymers. 相似文献
53.
Effect of Zwitterionic Surfactants on Interparticle Forces, Rheology, and Particle Packing of Silicon Nitride Slurries 总被引:1,自引:0,他引:1
William A. Ducker Erik P. Luther David R. Clarke Fred F. Lange 《Journal of the American Ceramic Society》1997,80(3):575-583
Phosphocholine (PC) zwitterionic surfactants, with different hydrocarbon chain lengths (C6 C6 PC to C9 C9 PC), were absorbed on the surface of silicon nitride near the isoelectric point (pH 6). Adsorption of the surfactants changed the lateral and normal surface forces, the rheology, and the consolidation behavior of the particles. The normal force between two silicon nitride surfaces as a function of separation and the lateral (friction) forces were measured using an atomic force microscope (AFM). These measurements indicated that surfactant adsorption reduced the magnitude of the long-range attractive van der Waals force and produced a repulsive short-range force. Although the adsorbed layers provided a barrier to particle contact, they could be ejected with a critical force that increased with the hydrocarbon chain length. The effect of an adsorbed layer on the viscosity and consolidation of slurries was also measured. The viscosity of all slurries decreased with increasing shear rate, indicative of attractive particle networks. The highest viscosity was observed for slurries formulated at the isoelectric point without added surfactant. Much lower viscosities were observed when the surfactant concentration was greater than the critical micelle concentration (cmc). A relative density of 0.46 was obtained via pressure filtration at 4 MPa without a surfactant, and between 0.46 to 0.59 (C6 C6 PC to C9 C9 PC, respectively) for surfactant concentrations greater than the cmc. Comparing force measurements with rheology and packing density provides a basis for discussing the role of interparticle forces in ceramic powder processing via colloidal routes. 相似文献
54.
Von Günter Kaufmann 《大分子材料与工程》1970,10(1):83-96
The importance of colouring matter is of prime importance in the plastics industry. The individual behaviour of organic pigments in the various polymer materials necessitates, however, on the part of the plastics manufacturer a precise knowledge of ?which pigment for which plastic”?. For example, a well known Thioindigo pigment behaves very differently in various polymer materials : In polystyrene, depending on the concentration used, it is monomolecularly dissolved, in associated solution or present as undissolved particles. In PVC, however, the good migration fastness is indicative of the insolubility of the pigment in this medium and so it is not surprising that PVC is the ideal plastic medium for this pigment. The behaviour of organic pigments in polymers is largely a function of molecular structure, e. g. intermolecular H-bonds can cause a decrease in solubility of a pigment in a polymer material, which in turn results in improved migration fastness. This is demonstrated by the improved migration fastness of variously substituted β-hydroxy naphthoic acid arylamide derivatives. Many phenomena exist however, which as yet can only be explained on the basis of the crystal structure of the pigment particles, i. e. the presence of aggregates or agglomerates. Such a phenomenon is, for example, the dispersibility of pigments in polymers. Here pigment surface, wettability by polymer and intermolecular forces are all of importance. In general, the dispersibility is better the smaller the specific surface area, as is shown for a typical quinacridone pigment. The influence of the rate of wetting on dispersibility is demonstrated using polyethylene wax. A further effect, which demonstrates the intermolecular forces between pigment and polymer, is the way in which certain pigments influence the rate of crystallization of partly crystalline polymers. This itself is connected with the shape and size of the pigment particles embedded in the polymer material. Such effects are demonstrated by measurements on various polyethylene objects. The pigment in this case was a naphthalene tetra carbonic acid derivative in both cis and trans form with widely varying specific surface areas. 相似文献
55.
The selfdiffusion coefficients of acetone and benzene are studied in the systems acetone/poly(methylmethacrylate) and benzene/poly(methylmethacrylate) by means of the spin echo technique as function of concentration and temperature. From the dependence of temperature, the activation energies are calculated as function of concentration. The dependence of concentration of the selfdiffusion coefficients is discussed using the theory of Free Volume according to FUJITA. The Free Volume of the poly(methylmethacrylate) is calculated as function of temperature. 相似文献
56.
Erik E Luther Fred F. Lange Dale S. Pearson 《Journal of the American Ceramic Society》1995,78(8):2009-2014
Two different methods are used to coat silicon nitride particles with an alumina precursor to make Si3 N4 behave like Al2 O3 in aqueous slurries. The first method involves the precipitation of an aluminum hydroxycarbonate from dissolved Al(NO3 )3 during the decomposition of urea. In the second method, dry silicon nitride powder is reacted with aluminum tri- sec -butoxide in hexane at room temperature. Both methods produce a coated powder in which the electrophoretic and rheological properties of aqueous slurries mimic those of alumina. When salt is added to slurries consisting of coated Si3 N4 powder, all rheological evidence suggests the presence of a short-range repulsive potential that produces a weakly attractive particle network similar to that previously reported for Al2 O3 powder. Although electrophoretic and rheological data showed that the coated powder behaved like Al2 O3 , consolidation data indicated that slurries of coated powder with added salt did not pack to high density. In addition, these bodies were not plastic as found for bodies consolidated from dispersed and salt-added Al2 O3 slurries. 相似文献
57.
3,7-Dimethyl-2-undecanol, 3,7,9-trimethyl-2-tridecanol, and 3,7, 11-trimethyl-2-tridecanol were synthesized as racemic mixtures in moderate yields. The alcohols are known precursors of the female sex pheromones of the pine sawfly species Diprion nipponica, Macrodiprion nemoralis, and Microdiprion pallipes, respectively. Stereoisomeric mixtures of 3,8,12-trimethyl-2-tridecanol, erythro-(2R,3R,11R/S)-3,11-dimethyl-2-tetradecanol, 3,5-dimethyl-2-tetradecanol, and 5,7-dimethyl-2-tetradecanol, structurally related to sex pheromone alcohol precursors of pine sawfly species, were also synthesized in moderate yields. The key reaction in the syntheses was the ring opening of -butyrolactones by using different alkyl lithiums as nucleophiles. 相似文献
58.
Erik Løvaas 《Journal of the American Oil Chemists' Society》1991,68(6):353-358
The antioxidative effects of spermine, spermidine and putrescine were determined by measurement of primary and secondary oxidation products of polyunsaturated fatty acids, using gas and liquid chromatography as well as spectrophotometric recordings. It was demonstrated that polyamines inhibit the oxidation of polyunsaturated fatty acids,α-tocopherol and carotenoid pigments. Both linear and nonlinear dose/response relationships have been observed. The efficiency of a given polyamine was correlated with the number of amine groups in the molecule. Spermine was, thus, more efficient than spermidine, which in turn had a higher efficiency than putrescine. The relative antioxidative effect was as follows: spermine (100.0), spermidine (61.0), putrescine (23.0), ethoxyquin (27.6), ascorbyl palmitate (18.3), octyl gallate (7.9), tert butylhydroquinone (6.3), butylated hydroxyanisole (3.6) andα-tocopherol (3.4). 相似文献
59.
M. J. Albrink R. M. Krauss F. T. Lindgren J. Von Der Groeben S. Pan P. D. Wood 《Lipids》1980,15(9):668-676
The interrelationships among fatness measures, plasma triglycerides and high density lipoproteins (HDL) were examined in 131
normal adult subjects: 38 men aged 27–46, 40 men aged 47–66, 29 women aged 27–46 and 24 women aged 47–66. None of the women
were taking estrogens or oral contraceptive medication. The HDL concentration was subdivided into HDL2b, HDL2a and HDL3 by a computerized fitting of the total schlieren pattern to reference schlieren patterns. Anthropometric measures employed
included skinfolds at 3 sites, 2 weight/height indices and 2 girth measurements. A high correlation was found among the various
fatness measures. These measures were negatively correlated with total HDL, reflecting the negative correlation between fatness
measures and HDL2 (as the sum of HDL2a and2b). Fatness measures showed no relationship to HDL3. There was also an inverse correlation between triglyceride concentration and HDL2. No particular fatness measure was better than any other for demonstrating the inverse correlation with HDL but multiple
correlations using all of the measures of obesity improved the correlations. Partial correlations controlling for fatness
did not reduce any of the significant correlations between triglycerides and HDL2 to insignificance. The weak correlation between fatness and triglycerides was reduced to insignificance when controlled for
HDL2.
Presented (in part) at the Annual Meeting of the Oil Chemists' Society in St. Louis, MO, May 1978. 相似文献
60.
Transient experiments were performed to study sulfur deactivation and regeneration of Pt/BaO/Al2O3 and Pt/SrO/Al2O3 NO
x
storage catalysts. It was found that the strontium-based catalysts are more easily regenerated than the barium-based catalysts
and that a higher fraction of the NO
x
storage sites are regenerated when H2 is used in combination with CO2 compared to H2 only. 相似文献