Von R. Bonart

Bio: Von R. Bonart is an academic researcher from Bayer. The author has an hindex of 2, co-authored 2 publications receiving 101 citations.

Zur kristallstruktur der polycarbonate aus 4,4′-dihydroxydiphenyl-2,2-propan, 4,4′-dihydroxydiphenylsulfid und 4,4′-dihydroxydiphenylmethan†

Abstract: Es wird gezeigt, das das Polycarbonat aus 4,4′-Dihydroxydiphenyl-2,2-propan monoklin in der Raumgruppe Cs2 mit je 4 Ketten in der Gitterzelle, das Polycarbonat aus 4,4′-Dihydroxydiphenylsulfid und das aus 4,4′-Dihydroxydiphenylmethan dagegen rhombisch in der Raumgrupe C2v9 mit je 2 Ketten in der Gitterzelle kristallisiert. Die Faseridentitatsperiode umfast in allen drei Substanzen jeweils zwei monomere Einheiten, so das je 8 bzw. je 4 monomere Einheiten in der Gitterzelle liegen. Die Kristalldichten sind 1,315 g/ccm fur das Polycarbonat aus 4,4′-Dihydroxydiphenyl-2,2-propan, 1,50 g/ccm fur das Polycarbonat aus 4,4′-Dihydroxydiphenylsulfid und 1,303 g/ccm fur das Polycarbonat aus 4,4′-Dihydroxydiphenylmethan. Die Faseridentitatsperioden der drei betrachteten Polycarbonate sind um ca. 15% bis 20% gegenuber ihrer theoretischen Maximallange bei voll ausgestreckten Ketten verkurzt. Dementsprechend betragt der Kristall-Elastizitatsmodul in Kettenrichtung ca. 450 bis 600 kp/mm2. Die betrachteten Kristallstrukturen enthalten keinerlei Gleitebenen, so das die Kristallbereiche eine hohe Scherfestigkeit besitzen. Die geringe Kristallisationstendenz des Polycarbonates aus 4,4′-Dihydroxydiphenyl-2,2-propan findet durch die Kristallstruktur eine plausible, zwanglose Erklarung. The polycarbonate from 4,4′-dihydroxydiphenyl-2,2-propane crystallizes monoclinically in the space group Cs2 with four chains each in the lattice cell, but the polycarbonate from 4,4′-dihydroxydiphenyl sulfide and from 4,4′-dihydroxydiphenyl methane crystallizes orthorhombically in the space group C2v9 with two chains each in the lattice cell. In all three substances, the fibre identity period always comprises two monomeric units, so that always eight and always four monomeric units, respectively, are located in the lattice cell. The crystal densities are 1.315 g./ccm. for the polycarbonate from 4,4′-dihydroxydiphenyl-2,2-propane, 1.50 g./ccm. for the polycarbonate from 4,4′-dihydroxydiphenyl sulfide, and 1.303 g./ccm. for the polycarbonate from 4,4′-dihydroxydiphenyl methane. The fibre identity period of the three substances, as compared with their theoretical maximum length in the case of fully stretched chains, has been shortened by 15 per cent to 20 per cent. Accordingly, the crystal elasticity modulus in the direction of the chain only amounts to about 450 to 600 kp./mm2. The crystal structures considered do not contain any glide planes, so that the crystal domains possess a high shear strength. The low crystallization tendency of the polycarbonate from 4,4′-dihydroxydiphenyl-2,2-propane is easily and plausibly accounted for by its crystal structure.

Struktur und eigenschaften von verstreckten polymeren (fasern)

Abstract: Im mechanischen Verhalten teilkristalliner Fasern uberlagern sich die elastischen und plastischen Eigenschaften der amorphen und der kristallinen Anteile. Die Art der Uberlagerung hangt von der Kolloidstruktur ab, d. h. von der gegenseitigen raumlichen Kristallitanordnung sowie von den Mechanismen der Kraftubertragung von Kristallbereich zu Kristallbereich. In einem qualitativen Uberblick werden einige der z. Z. diskutierten Modelle fur die Kolloidstruktur sowie fur die Kraftubertragung durch interkristalline Kettensegmente (tie molecules) zusammengestellt und mit den mechanischen Fasereigenschaften in Zusammenhang gebracht. Vergrobernd kann gesagt werden, das das elastische Verhalten im wesentlichen durch die Eigenschaften der amorphen Bereiche gegeben ist, wahrend das plastische Faserverhalten (das u. a. bei der Texturierung und dem Knitterverhalten eine wesentliche Rolle spielt) in hoherem Mase zusatzlich auch von der Eigenschaft der Kristallbereiche abhangt. Schallgeschwindigkeitsmessungen liefern wesentliche Informationen zum Mechanismus der Kraftubertragung zwischen benachbarten Kristallbereichen. The mechanical behaviour of synthetic fibres is controlled by a superposition of the elastic and plastic properties of the amorphous and the crystalline regions. The kind of superposition depends on the colloidal structure, i. e. on the spatial arrangement of crystallites as well as on the mechanism of power transfer from crystallite to crystallite. A qualitative survey is given of some nowadays accepted general features of the colloidal structure and of the power transfer by tie molecules corresponding to special fibre properties. Roughly speaking the elasticity of fibres is predominantly controlled by the amorphous regions. However being more important to false-twist yarns and crease-resistant fabrics the plasticity of fibres is highly influenced by the mechanical behaviour also of the crystalline regions. Additional information about the said power transfer follows besides others from the measurement of sound velocity.

Structure and properties of polyethyleneterephthalate crystallized by annealing in the highly oriented state

Abstract: The structure of polyethyleneterephthalate bristles drawn about five times in the amorphous state and subsequently crystallized at temperatures between 100 and 260‡ C has been studied by means of small-angle X-ray scattering. In addition density, heat of fusion and wide-angle scattering behaviour were measured. For comparison, similar experiments were carried out with undrawn samples. The results showed that the degree of crystallinity of PET cannot be calculated from density data on the basis of a simple two-phase model, since the effective densitiesρc* andρa* of the crystalline and amorphous regions depend strongly on crystallization and drawing conditions. With rising crystallization temperature the size of the mosaic blocks building up the crystalline layers and their longitudinal mutual order increase whereas the volume fraction of the crystalline region is only rather slightly effected by the annealing temperature. The difference between the effective densityρc* and the “X-ray density”ρc of the crystalline layers is supposed to be caused by lattice vacancies in the boundaries of the mosaic blocks.

Phase separation in urethane elastomers as judged by low-angle X-ray scattering. I. Fundamentals

Abstract: In thermoplastic urethane elastomers, phase separation between hard and soft segments resulting in a domain structure is an essential condition for a sufficiently high heat distortion temperature. The state of segregation, i.e., the domain structure, is characterized by the following aspects: 1) the size distribution, i.e., the dispersion level of the domains; 2) the sharpness of diffuseness of the domain boundaries, and 3) hard segments dissolved in the soft segment matrix or soft segments included in the domains. The state of segregation may be evaluated by means of low-angle X-ray scattering. The fundamental theory, based on Porod's theory of low-angle scattering, is given in this paper. Experimental findings will be discussed in a later paper.

Morphology-property studies of amorphous polycarbonate

Abstract: The relationship between morphology and several physical properties (tensile, thermal, dielectric, and dynamic mechanical properties) of amorphous poly-bisphenol-A-carbonate was examined as a function of annealingtime at temperatures below the glass transition temperature (Tg). The change in structure of the amorphous films was studied by means of X-ray diffraction and with electron diffraction using a rotating sector in an electron microscope as well as by electron micrographs of replicas of surfaces prepared by etching with dilute aqueous NaOH solutions. The changes in morphology and physical properties caused by annealing below Tg are, in general, closely related. The relationship cannot be explained only by changes in free volume; it is proposed that changes in the degree and type of order (nodular structure) also play a role. The design and application of the rotating sector is described in an Appendix.

Measurement of hole volume in amorphous polymers using Positron spectroscopy

Abstract: Positron annihilation lifetime spectroscopy (PALS) measurements, in the temperature range 110−480 K, are given for three linear, amorphous polymers. Based on these measurements, a method is proposed for evaluating the hole volume in amorphous thermoplastics. Our studies show that hole volume is composed of static and dynamic components. We demonstrate that the dynamic component, which is a result of the thermal vibrations of the molecular chains, is strongly correlated to thermodynamic volume/density fluctuations. The static hole volume is interpreted as “frozen-in” fluctuations, which are manifested as nanometer-sized flaws in the packing of molecular chains. The results from PALS measurements reported in our work are in very good agreement with results from small-angle X-ray scattering measurements.

Rheo-optical Fourier-Transform infrared spectroscopy: Vibrational spectra and mechanical properties of polymers

Abstract: The advantages of Fourier-Transform infrared (FTIR) spectroscopy over conventional dispersive instrumentation have revitalized the utilization of vibrational spectroscopy in polymer research. In the field of rheo-optics primarily the rapid-scanning capability of the FTIR technique has contributed to a more detailed insight into the technologically important process of polymer deformation. It is the purpose of this review to present the relevant instrumental and theoretical background of polymer deformation and relaxation studies by simultaneous FTIR spectroscopic and mechanical measurements and to summarize selected experimental results obtained by this technique.