Conductive polyethylene-carbon black composites by elongational-flow injection molding Part 3. Study of the structure and morphology

The morphology and structure of high molecular weight linear polyethylene (M _w 450000) filled with carbon black and processed using molds that introduce an elongational flow component during injection molding has been examined using electron microscopy and x-ray diffraction techniques. The study of fracture surfaces reveals the display of shish-kebabs oriented along the injection direction with segregated longitudinal channels of carbon black particles. Molecular and lamellar changes in orientation are, furthermore, studied across the thickness of the moldings. It is shown that addition of carbon black particles to injection-molded polyethylene induces significant changes in lamellar orientation. Thus, while lamellar overgrowth proceeds perpendicular to the fiber axes within carbon free channels, lamellae grow randomly within carbon-enriched regions where flow is less pronounced.     

On the Synthesis of cis-Tetramminecobalt(III) Complexes

The preparation is described of cis-tetramminebis(dimethylformamide)cobalt(III) and cis-tetramminebis(trifluoromethanesulfonato)cobalt(III) complexes. The compounds were studied as starting materials for the synthesis of other tetrammine compounds formed by substitution processes which are based on the reactivity of the ligands.     

Dielectric relaxation of poly(ester-ether-carbonate) multiblock terpolymers

The dielectric properties of a series of poly(ester-ether-carbonate) multiblock terpolymers have been investigated as a function of ether and carbonate composition in the frequency range of 10³–10⁶ Hz. The degree of polymerization of the samples was determined by viscosimetry measurements. The weight fraction, degree of crystallinity, and melting temperatures were characterized by means of x-ray diffraction and DSC methods. Dielectric behavior has been discussed in terms of Havriliak-Negami formulation. The variation of the dielectric properties with temperature has been associated with two relaxation processes: a) the -relaxation process observed at low temperature, which is associated to local motion of polar groups attached to both the soft and the hard segments, and b) the process assigned to long-range molecular motions above the glass transition temperature.     

Influence of photogeneration centers on the intensity of a thermally stimulated current transport peak. Application to poly(N-vinylcarbazole)

The influence of coulomb centers (coulomb traps and photogeneration centers) on the intensity of a thermally stimulated current (TSC) transport peak is examined. We apply these concepts to account for the field dependent transport charge associated to the area under the TSC traces resulting from poly(N-vinylcarbazole).Dedicated to Professor Dr. F. H. Müller.     

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

The application of thermodynamics of eutectoid copolymers and a generalized Tabor-relation to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by results on melt-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despite being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries (meso-crystals) which yield cooperatively.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.     

Influence of processing methods on starch properties

Native potato starch was prepared using different processing methods. The samples were characterized by wide-angle X-ray scattering (WAXS), optical microscopy, differential scanning calorimetry (DSC), and microhardness. Compression molding of the starch granules led to sintered relatively brittle materials. Here, the amylopectin crystals of the native powder remained grossly preserved. Preparation of dry films from aqueous gels resulted in disintegration of the structure of the native starch granules and in the formation of a new semicrystalline structure comprised of crystallized amylose molecules. Injection molding of native starch was found to be a processing method that gives rise to amorphous materials with superior mechanical properties.     

X-ray diffraction study of bulk poly N-substituted maleimides

Summary A series of 7 aliphatic and 6 aromatic poly N-substituted maleimides (PNMI) was synthetized by free radical polymerization. The series was characterized by means of intrinsic viscosity, number average molecular weight and glass transition temperature measurements. The X-ray diffractograms of all samples show two rather broad maxima indicative of non-crystalline structures. The location of the innermost peak strongly depends on the length of the substituted groups and can be associated to intermolecular vectors. The observed linear increase of the spacing associated to the inner maximum with the number of methylene groups of the substituted aliphatic chain favours the idea of predominantly extended lateral conformations. The outer peak due is to intramolecular average distances along the backbone chain and slightly depends on the shape of the substituted groups. This repeat distance fits well with the assumption of a 4/1 helix for the chain conformation. In the aryl series a third maximum appearing as a shoulder on the outer peak suggests the presence of chain sequences coiled in 3/1 helices. The chain bundle dimensions calculated from the broadening of the innermost maximum are of the order of two intermolecular vectors suggesting, hence, the absence of a well defined short range order. A model for the packing of PNMI molecules with lengthy substituted groups is proposed.

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Zusammenfassung Eine Serie von 7 aliphatischen und 6 aromatischen Poly-N-substituierten Maleimiden (PNMI) wurden mit radikalischer Polymerisation synthetisiert. Die Proben wurden mit Hilfe von Messungen der intrinsic-Viskosität, des Molekulargewichts-Zahlenmittels und der Glas-Temperatur charakterisiert. Röntgendiagramme der Proben zeigen zwei ziemlich breite Maxima, entsprechend der nichtkristallinen Struktur. Die Lage des inneren Piks hängt streng von der Länge der substituierten Gruppen ab und kann mit diesbezüglichen zwischenmolekularen Abständen verknüpft werden: Das beobachtete lineare Anwachsen des mit dem inneren Maximum verknüpften Abstandes entspricht nämlich der Anzahl der Methylengruppen in der substituierten aliphatischen Kette und weist darauf hin, daß sich die laterale Konformation vergrößert. Der äußere Pik entspricht mittleren intramolekularen Abständen längs der Kette und hängt nur wenig von den substituierten Gruppen ab. Die Distanz paßt zur Annahme einer 4/1-Helix-Konformation. In der Arylserie erscheint ein 3. Maximum, das auf das Auftreten von 3/1 Helices hinweist. Die berechneten Dimensionen von Kettenbündeln aus der Verbreiterung des inneren Maximums sind von der Größenordnung des doppelten inter-molekularen Abstands und zeigen somit an, daß keine wohldefinierte Nahordnung besteht. Ein Modell für die Packung der PNMI-Moleküle mit substituierten Seitengruppen wird vorgeschlagen.

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Dedicated to Prof. Dr.R. Hosemann on the occasion of his 60th birthday.