An investigation into the fracture behaviour of ethylene propylene impact copolymers

Injection moulded copolymer specimens containing between 6 to 11% ethylene were impacted using the drop weight method at 23°C and −20°C. Their response to the impact event was analysed in terms of failure mechanisms by considering their initiation and propagation energies at the respective temperatures. At −20°C, the results indicated that the multiple shear yielding toughening mechanism is predominant whereas room temperature tests show evidence of multiple crazing behaviour. The peak force sustained by the specimens decreased with the testing temperature.     

The application of molecular mechanics to the structures of carbohydrates

A study is reported of the accuracy with which the geometries of pyranose and methyl pyranoside molecules are predicted by molecular mechanics. Calculations of the conformational energies of the model compounds dihydroxymethane, methoxymethanol, and dimethoxymethane, made with the program MMI, produced results that compare well with previous ab initio molecular orbital calculations. This indicates that MMI gives a satisfactory account of the energetic and conformational aspects of the anomeric effect, a conclusion further supported by calculations on 2-methoxytetrahydropyran. The prediction of the observed preferred conformations of the primary alcohol group in aldohexopyranoses appears to be less satisfactory. MMI-CARB, a version of MMI with changes in some of the equilibrium C? O bond lengths of the program, has been used to calculate the geometries of 13 pyranose and methyl pyranoside molecules, the crystal structures of which have been studied by neutron diffraction. When the C? C? O? H torsion angles are constrained to approximately the values observed in the crystal structures, good agreement is obtained between the theoretical and experimental molecular geometries. The rms deviation for C? C and C? O bonds, excluding those significantly affected by thermal motion in the crystal structure determinations, is 0.005 Å. Corresponding figures for the valence angles that do not involve hydrogen atoms and for the ring torsion angles are 1.2° and 2.0°, respectively. The Cremer and Pople puckering parameters for the pyranose rings are reproduced within 0.026 Å in Q and 5.4° in θ.     

The behaviour of some ferrocene derivatives under electron impact

The behaviour of some mono- and di-substituted ferrocene compounds under electron impact has been investigated by means of low-resolution mass spectrometry. Some characteristic rearrangement processes have been observed and discussed.     

The fragmentation behaviour of some spirobenzthiazoles under electron impact

The electron impact induced fragmentations of ten spiro-benzthiazoles have been studied. The principal decomposition reactions have been elucidated by metastable studies, exact mass measurements, and by deuterium exchange of the imino hydrogen. The primary fragmentation step is an α-cleavage reaction, which leads to ring opening of the ring fused to the benzthiazole moiety of the molecule. The subsequent decompositions resemble those of cyclohexylamines. They follow a general pattern, the details of which are discussed with respect to the nature and position of the heteroatom in the saturated ring.     

An investigation of methods for the application of molecular mechanics to lanthanide complexes

Methods are described for molecular mechanics calculations on lanthanide complexes. The irregularity of the coordination spheres of these metals necessitate special treatment in a molecular mechanics force field. Three different methods for treating the metal coordination sphere in the complexes are evaluated. In the first method, we include bond stretch terms between metal and donor atoms and 1,3 interactions between donor atoms. The second method utilizes a nonbonded potential between metal atoms and donor atoms to determine the geometry of the coordination sphere, and the third method involves coulombic interactions as well as a nonbonded potential to describe the van der Waals interactions. Evaluations of the three methods have been carried out by calculating the r.m.s. deviations between experimental structures and minimized structures. Results indicate that it is possible to achieve good agreement by all three methods, but that the second method provides the most consistent results, as well as being relatively straightforward to paramaterize.     

The role of water in polyamides

Summary The influence of water content (during the actual measurement) on density, crystal and supermolecular structure of polyamid 6 and 6.6 has been investigated. The results indicate that the water molecules penetrate as well into the amorphous as into the crystalline regions. The increase in density due to the water content is found to be the higher the lower the initial density of the specimens is. The change of density takes a (partially) reversible course with the water content of the specimens.

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Zusammenfassung Der Einfluß des Wassergehaltes (während der jeweiligen Messung) auf die Dichte, die Kristall- und die übermolekulare Struktur von Polyamid 6 und 6,6 wird untersucht. Die Befunde deuten darauf hin, daß die Wassermoleküle sowohl in die amorphen wie auch die Kristallbereiche eindringen können. Die Dichtezunahme infolge des Wassers ist um so größer, je geringer die Ausgangsdichte der Proben ist. Die Dichteänderung verläuft (partiell) reversibel mit dem Wassergehalt der Proben.

     

The behaviour of intramolecular charge transfer complexes under electron impact

Mass spectra of the three series of intramolecular charge transfer complexes: pyridylethylated tetrahydro-γ-carbolines and indoles as well as dinitrobenzoyl derivatives of N-(aminoalkyl)indoles, show stabilities of molecular ions to increase with electron donor strength of substituents in the indole nucleus. The results obtained demonstrate that stabilities of molecular autocomplexes can be estimated from their mass spectra.     

New approach to synthesis of aromatic N-phenyl-substituted polyamides

It is shown that polyimidates obtained by polycondensation of bisphenols with imidoyl chlorides may be transformed into N-phenylsubstituted aromatic polyamides. The rearrangement occurs as a result of heating at 260–340°C, and, in a diphenyl ether solution, at 240°C. The resulting polymers are soluble in organic solvents and demonstrate high thermooxidative stability.     

Influence of structure on the impact behaviour of nylon-rubber blends

Blends of nylon-6 and EPDM rubber were prepared by reaction blending to study the influence of rubber concentration, rubber particle size and interfacial adhesion on the impact strength. Rubber particles induce a sharp brittle-tough transition which is independent of the glass transition of the nylon matrix. Increasing the rubber concentration or decreasing the particle diameter shifts the brittle-tough transition temperature for notched Izod impact tests to lower values. A toughening mechanism is proposed in which the interparticle distance, the rubber modulus and the temperature play crucial roles.     

The mass spectrometric behaviour of benzohydroxaraic and benzothiohydroxamic acids under electron impact

Primary fragmentation reactions in benzohydroxamic and benzothiohydroxamic acids have been studied and compared with those in benzamides and benzothioamides. Mass-analysed ion kinetic energy spectra, collisional activation spectra and spectral data from labelled compounds were used to elucidate fragment ion structures and reaction mechanisms. The mass spectra are shown to be dependent on ion source temperature. Losses of O and H₂O are proved to be thermal in origin. The formation of an S… HO bond, which is analogous to an intramolecular hydrogen bond in solution chemistry, directs many fragmentation pathways. This seems to be the major factor determining the differences between the mass spectra of benzothiohydroxamic acids and those of the corresponding carbonyl compounds.     

Pitfalls in the evaluation of impact fracture of polymer-based materials

The fracture behaviour of a number of short- and long-GF/polypropylene-based materials, long-GF reinforced nylon-6,6 and CF/epoxy composites was assessed using an instrumented impact tester. A meaningful assessment of the mechanical response of the specimens to the instrumented loading was shown to depend on the stability of the specimen support system and hence specimen resonance. The fracture properties (K_c and G_c) were in general independent of specimen dimensions and moulding flaws in the case of unfilled polypropylene. Fibre-containing systems demonstrated significant variation in the properties as a function of fibre distribution. Preparation of the test-pieces had a marked effect, particularly for specimens containing a high concentration of long fibres. An equivalent notch depth for specimens containing a machined notch and dispersed fibres is defined.     

From the Periphery: the genesis of Eugene P. Wigner's application of group theory to quantum mechanics

This paper traces the origins of Eugene Wigner's pioneering application of group theory to quantum physics to his early work in chemistry and crystallography. In the early 1920s, crystallography was the only discipline in which symmetry groups were routinely used. Wigner's early training in chemistry, and his work in crystallography with Herman Mark and Karl Weissenberg at the Kaiser Wilhelm institute for fiber research in Berlin exposed him to conceptual tools which were absent from the pedagogy available to physicists for many years to come. This both enabled and pushed him to apply the group theoretic approach to quantum physics. It took many years for the approach first introduced by Wigner in the 1920s – and whose reception by the physicists was initially problematical – to assume the pivotal place it now holds in physical theory and education. This is but one example that attests to the historic contribution made by the periphery in initiating new types of thought-perspectives and scientific careers.     

Heterochain polyamides Communication 6. Preparation of polyamides and amide-ester copolymers by the aminolysis of polyesters

Summary The aminolysis of polyethylene sebacate with 1,6-hexanediamine was investigated and it was found that exchange of ethylene glycol and 1,6-hexanediamine residues occurs with formation of amide-ester copolymers or polyamides, depending on the relative amounts of reactants.