Über die Eigenschaften einiger wasserlöslicher Azo-Initiatoren

Water soluble azo compounds of the structure 1a, b, 2a, b, 3, 4 , and 5 decompose, depending on the substitution of the aromatic ring, in water already at room temperature. Therefore, they are useful initiators for solution and emulsion polymerisations in this temperature region. Reactions competing with thermolysis, as the formation of a hydrazone (pH>8) and ionic reactions with suitable reagents (phenols) are described.     

Pulsradiolytische messung der geschwindigkeitskonstanten der kombination von polyäthylenoxid-radikalen in wäßriger lösung

OH radicals from the radiolysis of water attack dissolved polyethylene oxide to yield side-group macroradicals. The UV absorption of these radicals was investigated. The rate constant of combination of two macroradicals could be calculated from the measured decay of the absorption after a short pulse of radiation. It was determined for polyethylene oxide of various degrees of polymerization (2 to 3000). It decreases with increasing chain length. The results are compared with the theories of BENSON and NORTH and of BAGDASARIAN , in which the termination step of polymerizations is investigated as function of the chain length of the macroradicals.     

Experimentelle untersuchungen zur phasentrennung im ternären system polymeres/lösungsmittel/fällungsmittel. 2. Der fällungspunkt und die menge des gefällten polymeren

Experimental investigations on the precipitation behaviour of polymers in ternary systems polymer-solvent-nonsolvent gave the following results:

• 1 The dependence of the precipitation point – determined by the volume fraction of the non-solvent – on the logarithm of the polymer concentration is not found to be a linear function but a curve which is monotonic bended towards the log c-axis.
• 2 The amount of polymer precipitated by a distinct amount of added non-solvent can be calculated from this equilibrium curve.
• 3 The precipitation point of a polymer is not influenced by the amount, the molecular weight, and the molecular weight distribution of lower molecular weight parts. The precipitation of a definite degree of polymerisation in a polydisperse mixture is therefore not a function of the total concentration of polymer but of the partial concentration of this special component.

These results are discussed in the light of different theories describing the precipitation behaviour of polymers.     

Untersuchungen zum oxidativen abbau nativer cellulose, 4. Stöchiometrische verhältnisse zwischen der anzahl der entstehenden spaltstellen,dem sauerstoff-verbrauch,der CO2-entwicklung und den materialverlusten während des abbaus

An investigation of the kinetics of cellulose degradation confirms the scheme proposed by G. V. Schulz and Mertes with the following modifications: the fast pre-stage of the degradation is missing, because there are no faster cleaving bonds in the native cellulose; the first step of the degradation (pre-oxidation) in agreement with the above mentioned authors consists in the uptake of an oxygen atom: in the second step, the scisson proper, the scheme of Staudinger and Roos is replaced by the newer and better founded scheme of Haskins and Hogsed, assuming an alkoxy-elimination; the third step (post-oxidation) finally consists in a limited number of substeps leading to a splitting off of about three glucose units which becomes evident in the losses of material. The values of the rate constants of the three characteristic reactions determined from the steady-state and the non steady-state period of the reaction practically coincide.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 2. Die Abhängigkeit der Abbaugeschwindigkeit von der Polymergesamtkonzentration in guten Lösungsmitteln

Mechanical shear degradation of poly(decyl methacrylate), (viscosity average molecular weight in tetrahydrofuran M?_η = 1,3·10⁶, M?_w/M?_n = 5) in the thermodynamically good solvent tetrahydrofuran has been studied in turbulent flow through a capillary as a function of polymer concentration in the range from 0,22 to 8,9 g/100 cm³. Due to turbulent flow conditions the shear stress, shear rate and shear energy proved to be the same for all concentrations and remained constant during degradation, giving a general insight into mechanism of degradation. The rate of degradation has been followed using molecular weight distribution curves obtained by gel permeation chromatography. The reaction was found to be of first order. Rate constants determined for molecular weights from 3,2–9,5·10⁶ decreased with increasing concentration following a law of the type k_i = (K + b·c)^?1, K and b being constants for each molecular weight. Hydrodynamic volumes of polymer molecules have been calculated according to models of Rudin as function of molecular weight and concentration. It can be shown that rate constants of degradation and calculated hydrodynamic volumes are proportional for the whole range of molecular weight and concentrations up to 3,6 g/100 cm³. There is also a rather good proportionality between these rate constants and the volumes of polymer coils predicted by de Gennes. This result is an additional confirmation of the concept that hydrodynamic volume governs shear degradation of polymer solutions. Additional experiments show that this type of concentration dependence is also to be found for other polymers in other solvents.     

Acrylsäure-popcornpolymere, 2. Oberflächenstruktur der glasigen und der popcorn-polymeren

By scanning electron microscopy characteristical differences are shown in the surface structure of three types of polymers—opaque, glassy, popcorn—obtained by polymerization of acrylic acid in bulk and in mixtures with water. These differences are related to the mechanism of formation of the polymers.     

Modellrechnungen zur Lösungsmittel- und Polymerenabhängigkeit der thermodynamischen Eigenschaften von Polymerlösungen

A great number of measurements on polymer solutions showed that there exists a distinct correlation between chemical potential, entropy and heat of dilution. Calculations were carried out on different models (quasi-chemical approximation, theory of orientation effects, theory of corresponding states, etc.) and these results were compared with experimental values. The theory of corresponding states yields the most extensive applicability, whereas the other theories may be applied to special problems.     

Untersuchungen zur klärung der sensibilisierten photodegradation von polystyrol in lösungen, 2. Energieübertragungsphänomene

A new approach is presented to explain “the sensitized photodegradation effect”, which was observed in polystyrene solutions irradiated with the light of a mercury lamp of wavelength λ ≥ 270 nm. The radiationless electronic excitation energy transfer from solvent molecules as energy donors to polystyrene (PS) macromolecules is considered to be the main factor influencing the polymer photodegradation rate in solution. Possible mechanisms of the energy transfer are discussed, the total energy transfer rate in eight investigated PS-solvent systems is evaluated and compared with PS photodegradation rates, determined by light scattering in the first part of this series.     

Scanningelektronenmikroskopische Befunde zur Ausbildung der Hörhärchen in Helicotremanähe beim Meerschweinchen

We report on findings in guinea pigs with objectively tested normal hearing ability. At the apical end of the Corti organ only in the inner row of hair cells the stereociliae are detectable by scanning electron microscopy. Here the row is interrupted several times. Near the helicotrema we find first the inner row of the outer hair cells, then the middle row and finally the outer row. At the beginning of the D-turn their arrangement is disordered. Normally, at the basal end of the D-turn all rows of inner and outer hair cells show their typical formation. This finding should be taken into consideration when making a cochleogram for proving of experimental noise damages.     

Einfluß einer orientierung der moleküle auf die kinetik der kristallisation von polyethylenterephthalat

Amorphous samples of poly(ethylene terephthalate) were oriented by drawing at 92°C to different drawing ratios as well as by cold drawing. The kinetics of isothermal crystallization was determined in the range from 70°C to 115°C. The orientation of the samples was measured by the birefringence before crystallization. With increasing orientation also the rate of crystallization increases and the Avrami exponent n decreases from 3 to 1. The density obtained at the end of the crystallization process almost is not affected by the orientation. The results also indicate that some sort of order occurs already during the orientation process. The results are discussed. The birefringence does not change monotonically during crystallization.     

Die Bestimmung der Molekulargewichtsverteilung von nichtkristallisierenden Polymeren mit dem Elektronenmikroskop, 5. Bestimmung der Masse der Einzelmoleküle und Aufnahme der Molekulargewichtsverteilung

A method is described for the determination of the molecular weight distribution (MWD) of various polymers from electron microscopy pictures of their molecules. It is shown, that the number of molecules needed to construct the distribution is between 200 and 300. Furthermore, with macroscopic density of the polymer and the volume determined by electron microscopy, the correct mass of a single molecule is obtained. The method is demonstrated for samples of polystyrene and poly(methyl methacrylate) and the results are compared with those of GPC-measurements.     

Die Abhängigkeit der Taktizität von der Polymerisationstemperatur und von Lösungsmitteln bei nach radikalischem Mechanismus hergestelltem Polyvinylacetat

Polyvinyl acetate (PVAc) was polymerized according to a radical reaction mechanism with AIBN as an initiator at temperatures between ?60°C and 200°C. Additionally, polymerizations were effected in nine different solvents. The tacticity of the polymers obtained was determined from the methyl resonances of the NMR spectra. The best spectra were obtained from a 3–5% (wt./vol.) polymer solution in deuterochloroform at 100 Mc/sec. It was found that the tacticity of radically prepared PVAc is independent of the polymerization temperature and that an ideal atactic product is always formed. Moreover, in all solution polymerizations examined no influence of the solvent on the tacticity was found.     

Experimentelle untersuchungen zur phasentrennung im ternären system polymer-lösungsmittel-fällungsmittel. 1. Die zusammensetzung der sol- und gelphase bei der fällfraktionierung

The composition of sol- and gel-phases as formed during precipitation fractionation in various systems polymer-solvent-nonsolvent is examined analytically. It is shown that the polymer concentration in the gel-phase is independent of the initial concentration of polymer in the solution. The polymer concentration of the gel-phase increases with increasing molecular weight, if the nonsolvent-solvent-ratio is kept constant. The nonsolvent-solvent-ratio in the gel-phase is always smaller than in the corresponding sol-phase, it is constant during the early steps of fractionation and decreases slightly at the end of fractionation.     

Möglichkeiten zur gezielten Manipulation der Genexpression des mikrobiellen Sekundärstoffwechsels

The present review deals with some theoretical and applied aspects of directed manipulations of control mechanisms governing the expression of microbial secondary metabolism. In attempting to make broad generalizations, the production of secondary metabolites is discussed in terms of the cellular differentiation of relevant organisms. On the basis of the actual information about the regulation of microbial idiolite synthesis, some potential ways for the quantitative and the qualitative improvement of secondary metabolite production are discussed. A number of examples demonstrate the effectiveness of rational strategies of strain development, e. g., the removal of non-specific repressions of secondary metabolism by environmental factors, the excessive production of precursors due to altered control of intermediary metabolism, the increased resistance of producer organism against the autotoxicity of some idiolites, the deletion of alternative pathways of the primary and secondary metabolism, manipulations concerning the product spectrum, the deletion of feedback mechanisms, and elimination of degradating pathways in the secondary metabolism etc. The scope and limitations of rational strategies of strain improvement by genetic and physiologic manipulations are subjected to final discussion.     

Untersuchung der teilschritte der ethylen-hochdruck-polymerisation, 1. Druckabhängigkeit der einzelnen geschwindigkeitskonstanten

In order to calculate the average molecular weight, the molecular weight distribution or the branching of low density polyethylene, the individual values of the rate constants of the different reactions involved in the free radical polymerization are required. The method of rotating sector was applied to determine the rate constants of chain propagation and chain termination in a wide range of temperatures and pressures. This first part of the work reports the influence of the pressure. It was found that the rate constant k_p of the chain propagation increases with rising pressure whereas the rate constant k_t of chain termination decreases. The effect of the pressure on k_p can be explained in terms of the activation volume. The decrease of k_t with pressure is caused by a diffusion controlled termination reaction.