Struktur und eigenschaften von ABS-polymeren. VIII. Das elutionsverhalten von homo- und copolymeren aus styrol und acrylnitril in der gelchromatographie. Aufstellung einer eichkurve für lösungsmittel unterschiedlicher güte

The elution behaviour in gel chromatography was investigated for a series of polystyrene, polyacrylonitrile and styrene acrylonitrile copolymer fractions with acrylonitrile contents of 12, 25 and 52% by weight. In each series of tests a separate calibration relationship for solutions in chloroform and dimethyl formamide (DMF) is obtained by plotting the molecular weight versus the elution volume. Using the hydrodynamic volume and undisturbed coil dimensions one can obtain universal calibration relationships, except for solutions of polystyrene in DMF. This exception is explained by the poor solubility of polystyrene in DMF, which necessitates taking into account the interaction between the polymer and solvent molecules. By plotting the product of the second virial coefficient and the molecular weight versus the elution volume a universal calibration relationship is obtained for all the differing series of solutions in chloroform; the differences between the solutions of polystyrene, the copolymers and polyacrylonitrile in DMF can be substantially reduced.     

Struktur und eigenschaften von Raney-Nickel-katalysatoren mit zulegierungen für alkalische brennstoffzellen

As is well known the catalytic activity of Raney nickel may be increased by alloying with some percentage of transition metals eg Fe, Ti, or Mo. Electrocatalysts activated in this way may reach exchange current densities up to 5 A/g, and in the anodic oxidation of H₂ current densities up to 4 A/g at 23°C. Sorption measurements and pore distributions calculated from the sorption isotherms show that the structure of the Raney sponge is changed but little by these transition metal additions; by the observed small structure differences the different properties of electrocatalysts cannot be explained. Discussion of these results shows that the measured high exchange current densities alone do not account for the high anodic current densities, because the diffusion of molecular hydrogen through the transitional pore system of the Raney sponge filled by electrolyte to the reaction zone does not admit current densities of more than 1 A/g. Only additional diffusion of chemisorbed H-Atoms on the catalyst surface allows the high current densities observed. Therefore an essential condition of a good electrocatalyst surface is a large coefficient D₀ of the surface diffusion of hydrogen exceeding 5 × 10⁻⁹ cm²/s.     

Struktur und eigenschaften von ABS-polymeren. III.. Charakterisierung der pfropfcopolymerisate von styrol-acrylnitril auf polybutadien durch oxydativen abbau

Graft copolymers of styrene-acrylonitrile on polybutadiene are isolated from the mixture with styrene-acrylonitrile copolymer formed during the graft copolymerization and are subjected to an oxidative degradation with potassium permanganate. The styrene-acrylonitrile copolymer grafted onto the polybutadiene can be isolated from the oxidation residue; it is, hence, accessible to further investigations. By blank runs it was verified that the styrene-acrylonitrile copolym er is not degraded under the oxidative conditions chosen. The increased content in carboxyl groups of the styrene-acrylonitrile copolymer isolated after oxidation of the polybutadiene grafted with it is attributed to fragments of the degraded graft basis.     

Struktur und eigenschaften von ABS-polymeren. IX. Quantitative untersuchungen zur morphologie von ABS-polymerisaten

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.     

Struktur und eigenschaften von simultanvernetzten bismaleimidmodifizierten novolak-epoxidharzen

N,N′-4,4′-Diphenylmethane-bismaleimide (BMI) was oligomerized in semisolid phenolnovolak epoxide-resin (EP) up to P?_n = 10. The morphology of the novolakcured EP-BMI solid resins is a two-phase structure. It consists in a homogeneous EP-BMI phase of an interpenetrating polymer network (IPN) and a BMI phase. The dynamic-mechanical properties depend on the overall weight fraction w₂ of BMI and on the degree of oligomerization (P?)_n of BMI. The relative shear modulus of the EP-EMI resin in the rubber state shows that both phases can be coherent. The glass transition temperature (T_g) can be correlated with the degree of oligomerization of the BMI, for instance Δ P?_n ≡ 10 corresponds to Δ T_g ≡ 35 K and Δ w^x₂ ≡ 0,25 (weight fraction of BMI in the homogeneous EP-BMI phase). Surprisingly, the breaking strength remains constant.     

Struktur und mechanische eigenschaften von hochorientierten polymeren

Correlations between the structure and main mechanical properties of highly oriented linear and laminar polymer structures (fibres, films, needle crystals) are considered. To discuss structural conditionality of mechanical properties, different typical linear polymers having different molecular structure and values of intermolecular interactions are taken as, for example, polyethylene, polypropylene, polyvinyl alcohol, polyacrylonitrile, polyamides, polyesters, cellulose, aromatic polymers and laminar structures as, for example, graphite, boron nitride, silicon carbide. A number of physical and mechanical characteristics of fibres from the above polymers is compared with their structure. Calculation methods of strength and elastic properties of highly oriented polymer materials on the basis of their structural characteristics are given. Extreme mechanical properties of oriented polymer systems are fairly high. Theoretical strength values (at absolute zero temperature) for various polymers are from 600 to 13 000 kp/mm². On the basis of the data of temperature-time dependence of oriented polymers the ultimate strength values have been estimated, i. e. strength values of samples with the ideal structure a t a given temperature and time of destruction. These values are approximately from 1/3 to 4/5 of theoretical strength values (at room temperature and the time of destruction of 10 see). The values of ultimate elastic moduli of oriented linear polymers are up to 25 000 kp/mm², and more than 100 000 kp/mm² for laminar structures. The article summarizes experimental data about physical and mechanical properties of polymer monocrystals and practically obtained mechanical properties of man-made fibres. Relations between strength and elastic properties of oriented polymer substances have been also considered. Data on anisotropy of mechanical properties of oriented polymers as a function of anisotropy of their structure and heterodynamics of energy interactions are reported. Principal conditions determining the applicability of various polymers for preparing high modulus and super strong fibrous polymer materials have been analyzed.     

Struktur und eigenschaften von mehrphasenkunststoffen. Deformations- und bruchverhalten von polycarbonat/ABS-mischungen

PC/ABS-blends have gained growing importance as engineering plastics in numerous different application sectors by the realization of interesting property combinations. These blends are in use for a longer time, but the literature about the basic physical aspects is not very comprehensive. The here presented work examines the influence of sample composition on phase behavior, on yielding and notched impact behavior. Sample composition is changed by mixing different amounts of PC, SAN and grafted rubber (polybutadiene rubber grafted with SAN). The yielding and impact behavior is discussed in connection with the deformation mechanisms. A subsequent paper will deal with the deformation morphology of these blends.     

Struktur und eigenschaften verschieden hergestellter hochdruckpolyäthylene

Low density polyethylenes (LDPE) synthesized under variable polymerization conditions, e.g. in a tube reactor (type R), have molecular structures considerably different from those of LDPE-samples with similar melt indices and densities which were polymerized under constant conditions, e.g. in a stirred autoclave reactor (type A). Thus, R-type products have narrower molecular weight distributions and wider distributions of short- and long-chain branching than A-type samples and show decreasing branching with increasing molecular weight. Moreover, there are differences in the structure of long-chain branching and in the molecular shape between R- and A-products. The results of measurements may be interpreted assuming that the A-type molecules have tree-like branched structures and approximately globular shapes whereas R-type molecules show comb-like branching and elongated rod-like shapes. The differences in the molecular structure lead to different supramolecular structures - e.g. narrower distributions of densities in spite of wider short-chain branching distributions with R products as compared with A-products-and to different physical and technological properties of the two LDPE-types synthesized in different ways. The results may be interpreted in terms of reaction kinetics. By a new modified autoclave process the molecular structures and the physical and technological properties of low density polyethylenes may be varied within wide limits.     

Rheologische eigenschaften für isotrope linear-viskoelastische kompositmaterialien

The article describes a method of determining the rheological properties which are associated with an uniaxial state of stress on an isotropic two phase material. It is assumed that the composite is composed of particles in a continuous matrix. Both phases are linear viscoelastic and the contact between them is supposed to be perfect. The method is demonstrated in examples concerning cement and asphalt concrete. Among other things, the influence of aggregate on the creep function and the complex Young's modulus is examined.

Zusammenfassung

Eine Methode zur Bestimmung der rheologischen Eigenschaften eines isotropen Materials unter einachsigem Spannungszustand, das sich aus zwei Phasen zusammensetzt, wird beschrieben. Es wird angenommen, daβ das System aus diskreten Teilchen in einer zusammenhängenden Matrix besteht. Beide Phasen seien linear viskoelastisc und seien vollkommen mit einander verbunden. Die Brauchbarkeit der Methode wird beispielhaft an Zement- und Asphaltbeton aufgezeigt. Unter anderem wird der Einfluβ des Zuschlages auf das Kriechen und auf den komplexen Elastizitätsmodul untersucht.     

Wasserstofferzeugung für die Hydrierung von Fetten und Fettsäuren

Production of Hydrogen for the Hydrogenation of Fats and Fatty Acids A process is described for the production of highly pure hydrogen from hydrocarbons, such as natural gas, liquefied gas and light petroleum. The process consists of following three steps: 1. Desulfurization of the starting material; 2. Conversion of hydrocarbons into permanent gases by splitting with steam at high temperatures; 3. Separation of other gases from hydrogen by adsorption. This process has been tested commercially. With increasing cost of transport, and owing to regulations for the transport of hydrogen, which are difficult to fulfil, the aforesaid process offers an attractive alternative to the consumer of hydrogen. Cost of investment, energy consumption and economy of the process are dealt with.