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 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 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 II.. Grenzviskositäts-molekulargewichtsbeziehungen für azeotrope styrol/acrylnitril-copolymerisate

Limiting viscosity numbers of azeotropic copolymers of styrene and acrylonitrile were measured in dimethylformamide (DMF) and in methyl ethyl ketone (MEK). Their weight average molecular weights (10⁴ g/mole ? M_w ? 10⁶ g/mole) were determined by light scattering. The viscosity – molecular weight relationships obtained, are for DMF and for MEK The number average molecular weights were determined by osmotic pressure measurements, and now molecular weight heterogenities were calculated. The homogenity in composition was investigated by light scattering measurements in different solvents. In addition the viscosity-molecular weight relationship for polystyrene in DMF was determined and compared with the relationship for the azeotropic poly (styrene-co-acrylonitriles) and for polyacrylonitrile: On account of the results a possibility is shown for calculating molecular weights of poly (styrene-co-acrylonitrile) of any composition from limiting viscosity numbers and the acrylonitrile contents.     

Herstellung und eigenschaften von cellulosebenzoat

Cellulose benzoates with degrees of substitution between 2.8 and 2.9 were synthesized in a one-step reaction of cellulose with benzoyl chloride in presence of pyridine as base. Their molecular weights were in the range 140000–100000; the glass transition temperature and the melting temperature were 155 and 274°C, respectively. The esters are readily soluble in organic solvents such as N,N-dimethyl formamide, chloroform and dichloromethane and show good thermal resistance up to 250°C. Because of the brittle character of cellulose benzoate, plasticizer (diethyl phthalate) must be added for the fabrication of films and workable, moulded parts. As shown by stress-strain and impact measurements, the hard and brittle character is retained for plasticizer contents up to 20 wt.-%.     

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.     

Synthese und eigenschaften von cycloaliphatischen glycidylestern

Diglycidylesters of cycloaliphatic dicarboxylic acids can be prepared in a good yield by the catalytic action of quarternary ammonium salts, or less universally also of thioethers. A considerable attention should then be especially paid to dehydrochloration. In comparison to epoxy resins from bisphenol A, it is an advantage of these products to have lower viscosity, higher reactivity with anhydrides, acids, and dicyandiamide, and excellent insulating properties, especially as far as are and track resistances are concerned. The best properties were found in diglycidylester of hexahydrophthalic acid, which are also less toxic. A disadvantage is a lower heat distortion point and a lower alkali resistance.     

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.     

Die kristallisation von polybutylenterephthalat (PBT) und polycarbonat (PC) im polymerblend PBT/PC

The crystallization behavior of PBT as well as PC is changed in the controlled-processed blend due to intermolecular interactions between the different macromolecules in molten state. If the kinetics of the crystallization process prevents a crystallization-induced separation, the partial miscibility of the amorphous phases, measured by the glass transition temperatures, will lead to a decrease of the crystallinity of PBT. The crystallinity, normalized to the concentration of PBT in the blend, is independent from the concentration of PC at low coolling rates. At high cooling rates, PBT is crystallizing stepwise in the blend PBT/PC 40/60 wt.-%. The crystallization temperature in the anisothermic crystallization process is increased at low contents of PC due to a changed nucleation mechanism. The half-time of crystallization is increasing in blends with an increasing PC-content in isothermic crystallization experiments. The normally amorphous PC crystallizes considerably fast in presence of PBT in PC-rich blends. The crystallization or change in the state of order of PC was measured in situ by X-ray diffraction. Calorimetric experiments confirm this result and allow a quantitative estimation of the PC-crystallinity, which amounts to some 20% in the blend PBT/PC 5/95 wt.-%.     

Zusammenhang zwischen physikalischer struktur und textilen eigenschaften von faserneuentwicklungen

By means of a series of methods of investigations, especially of X-ray wide and small angle scattering, the so-called supermolecular structure of synthetic fibres can be detected. From aromatic polyamides on the oné hand mainly amorphous fibres with a high water absorption can be produced while on the other hand fibres with an extremely high elastic modulus are obtainable. Polypropylene and polypivalolactone filaments show elastomeric character due to a special micromorphological lamellar structure.     

Struktur und Eigenschaften von Mehrphasenkunststoffen II. Kautschukmodifizierte Polycarbonate

Commercial polycarbonates are based on bisphenol A. They have high impact strength combined with high heat distortion temperatures. Polycarbonates based on other bisphenols mostly show low impact strngth whereas other properties often are improved; e.g. tetramethylbisphenol A-polycarbonate (TMBPA-PC) is characterized by high second order transition temperature (205°C), a good saponification stability, but its impact strength is not sufficient for some applications. Its impact strength can be improved by modification with styrene grafted rubbers. As a consequence of the compatibility of TMBPA-PC and polystyrene the polymer blends have high heat distortion temperatures excellent processibility and good impact strength. Due to the relatively low refractive index (n = 1.546) transparent blends can be achieved.     

Thermische und mechanische eigenschaften von polyurethanen mit mesogenen diolkomponenten

Nonsegmented and segmented polyurethanes (PURs) containing 4,4′-di(ω-hydroxyalkoxy)biphenyls were synthesized and the effect of the spacer length of the mesogenic diol on thermal and mechanical properties was investigated. DSC measurements showed similar thermal transitions for the segmented and the nonsegmented PURs. However, for the segmented PURs a shift to lower temperatures was observed. Polarization microscopy indicated the existence of LC phases in the nonsegmented PURs. The moduli of films of segmented PURs increased with growing length of the spacer, particularly at temperatures ≤40°C, due to decoupling of motions of the mesogenic and the urethane part. Decoupling also promotes formation of larger domains of the mesogenic groups. Flow was observed above a temperature dependent critical stress value. Chemical cross-linking below the thermal transitions improved the mechanical film properties as the physical network, due to domains of the mesogenic groups, superposes the chemical network. This was demonstrated with a PUR containing COOH groups crosslinked with a melamine resin at temperatures below or above the thermal transitions.     

Deformations- und Bruchmechanismen in mehrphasigen Polymersystemen

Firstly a short survey is given on the deformation and fracture mechanisms which are essential with respect to the mechanical behaviour of thermoplastics, i.e. on the quasi-brittle fracture, the fracture after shear yielding, and the fracture after yielding owing to crazes. Then the general fracture and flow criteria are treated that are applicable to polymer materials under multiaxial stress. In rubber-modified polymer systems the initiation and the growth of crazes work as the most important deformation mechanisms. Therefore the problems relating to them are discussed more detailed. Since the mechanical properties of rubber-modified systems are strongly dependent on the type and the morphology of the rubber phase, the next chapter deals with the problems in this field. In this connection also the interactions between the two deformation mechanisms—shear yielding and deformation by crazes—are important Finally a historical survey on the observations and theories of rubber toughening is given in an annex.     

Herstellung und eigenschaften von pfropfcopolymerisaten des vinylacetats auf ataktischem polypropylen

The applicability of atactic polypropylene is investigated in the graft polymerization with vinyl acetate. The obtained graft products with different compositions are characterized with reference to swell behaviour, glass transition temperature and graft parameters. After compounding of the graft products with polyvinylchloride the mechanical properties are represented in relation to the quantity and composition of the incorporated graft products.     

Struktur und Eigenschaften von ABS-Polymeren. XIV. Additiv-Effekte in ABS

Different types of ABS polymers are used as examples for demonstrating the influence of additives like emulsifiers, plasticizers and special oils on the glass transition behaviour of the polymer components and also on the interaction between the phases. These effects in combination with the resulting change of certain macroscopic properties must be taken into account for a critical comparison of polymer multiphase systems.     

Einfluß der struktur auf einige eigenschaften von polyurethan- und polyestermelamin-lacken

A method for calculating the crosslink density of systems originating from low molecular weight compounds is described. It is possible to determine quantitatively the influence of the crosslink density and the chemical composition on the glass transition temperature of network structures. This will be illustrated by crosslinked polyurethanes. On polyester melamine resins it will be shown that both the molecular weight of the polyester and the crosslink density of the network play an important role in the development of high solids coating systems as far as the solids content and the sagging are concerned.