Search Results

You are looking at 1 - 10 of 18 items for

  • Author or Editor: A. Schneider x
  • All content x
Clear All Modify Search

It is evidenced that due to the kinetic character of the glass transition as a ‘freeze in’ process, PVT measurements extended over the glass transition range depend not only on the thermal history but also on the pressure acting during the formation of the polymeric glasses. As a consequence metastable glasses are formed which show during heating of the glassy polymer through the glass transition range ‘volume relaxation zones’, characterized by a retarded increase or even decrease of the volume. The width of the ‘relaxation zone’ increases with increasing pressure and depends additional on the mode of operation used during the PVT measurements. In the same time a pressure induced shift of the glass temperature to higher temperatures is observed, the shift being the greater the stiffer the polymer, i.e. the higher the glass temperature of the polymer at atmospheric pressure. Due to the metastable character of polymeric glasses the evaluation of universal equations of states is thus not ingenious for polymeric glasses, because the deduced EOS will be valid only for that given glass characterized by a well defined thermal and pressure history. Additionally the EOS is influenced by the unknown time dependent aging and relaxation processes within polymeric glasses.

Restricted access

Isothermal and isobaric PVT-measurements of anionic polystyrenes

‘Relaxation zones’ within the glass transition range

Journal of Thermal Analysis and Calorimetry
Authors: A. Eckstein and H. A. Schneider

PVT-measurements of anionic polystyrenes on heating have shown that, depending on the mode of operation, specific ‘relaxation zones’ within the glass transition range are observed. Isothermal PVT curves exhibit always ‘relaxation zones’ independent whether the pressure is increased or decreased during the scan. The shift of the relaxation zones to higher temperatures is, however, higher for isothermal scans with increasing pressure. These ‘relaxation zones’ are explained by pressure-dependent changes of the state of the polymeric sample isothermally scanned within the glass transition range. At lower pressures the polymer is actually in the molten state, whereas at higher pressures it may be in the metastable glassy state and the actual state depends on the rate of pressure change. In isobaric PVT curves ‘relaxation zones” in heating scans are exhibited only if the pressure applied during glass formation differs from the pressure applied during the heating scan. The observed pressure-dependent shift of the glass temperatures to higher temperatures was higher for the studied polystyrenes of different molecular weight that had a higher glass temperature at normal pressure. But the specific molecular weight influence on the width of the ‘relaxation zone’ could not be ascertained. An attempt to calculate characteristic volume relaxation times failed because of insufficient precision of the measurements.

Restricted access

Several molecular markers have been reported for the detection of the 1RS chromosome arm. The aim of the present experiments was to study the reliability and reproducibility of six molecular markers specific to the 1RS rye chromosome (GPI, Bmac213, 5S, IAG95, SCM9 and RMS13) in distinguishing between wheat genotypes with and without the 1BL.1RS or 1AL.1RS translocations. In the course of the analysis, PCR products of the expected size were obtained with all the markers, which were found to give a reliable indication of the presence of the 1RS chromosome arm in the wheat genome.

Restricted access

Six different 1RS-specific molecular markers (RMS13, Bmac213, GPI, 5S, SCM9, IAG95) were tested in twenty rye cultivars of various origin. The aim of the experiments was to choose rye cultivars which give polymorphic PCR products with these 1RS-specific markers compared to the wheat cultivar Mv Magdaléna, which contains the 1BL.1RS translocation. The polymorphic rye cultivars can be presumed to differ from the 1BL.1RS translocation originating from the Petkus rye cultivar and will hopefully carry effective resistance genes which can be incorporated into the 1BL.1RS translocation in wheat. Twenty rye cultivars (at least two plants per cultivar) were analysed with these markers. Of fifty-two rye samples analysed, three plants were found to be polymorphic, one (Kisvárdai Alacsony from Hungary), for the 5S marker, one (Kriszta from Hungary) for the RMS13 marker and one (Porto from Portugal) for the SCM9 marker. The polymorphic plants were grown to maturity in the phytotron.

Restricted access

The formulae suggested for a series of complexes of Pd(II) with various amino acids have been verified by thermal methods using a derivatograph. A correlation of the obtained kinetic parameters with the structures suggested by electronic and IR spectra of the substances has been attempted.

Restricted access

One way of incorporating useful traits from Aegilops biuncialis (2n=4x=28, U b U b M b M b ) into wheat ( Triticum aestivum L. 2n=6x=42, AABBDD) is to develop first addition then translocation lines. The 2M b , 3M b , 7M b , 3U b , 5U b and 5U b /6U b wheat- Ae. biuncialis addition lines were produced in Martonvásár. To facilitate the exact identification of the addition lines, it was necessary to analyse the fluorescence in situ hybridisation patterns of the parental wheat genotype, Ae. biuncialis and its diploid progenitors ( Ae. umbellulata 2n=2x=14, UU and Ae. comosa 2n=2x=14, MM). The great genetic variability of the Aegilops species causes polymorphism in the fluorescence in situ hybridisation (FISH) patterns of the individual chromosomes. Due to the high level of FISH polymorphism, it is advisable to confirm the identification of the Ae. biuncialis chromosomes with the help of molecular (microsatellite, SSR) markers, so 119 wheat SSR markers were tested on Aegilops biuncialis , on Ae. geniculata (2n=4x=28, U g U g M g M g ), on five wheat- Ae. biuncialis addition lines (2M b , 3M b , 7M b , 3U b , 5U b ) and on an addition series of wheat- Ae. geniculata in order to select SSR markers specific to the U and M genomes of Ae. biuncialis and Ae. geniculata .

Restricted access

A method for determining the variation of the kinetic parametersA, E andn is proposed, and is exemplified by a study of PVC degradation, with the chlorine partially substituted by benzene. Because of the complexity of the method, a digital computer has been used.

Restricted access

The method of computer-experiments can be applied successfully on the radical depolymerization under inclusion of initiation, depropagation and termination. The comfortable PC-program ‘TA-kin’ for the non-linear estimation of parameters for TG- or DSC-experiments was applied to the determination of activation parameters of depropagation and termination. Therefore the overall-evaluation of three or more data sets is a prerequisite. The determination of kinetic parameters runs satisfactory if the measured curves are strongly different, e.g. by varying the heating rate, including acceptable experimental errors. Several recommendations for laboratory experts are given. A great support for a very sufficient estimation is the inclusion of simultaneous analysis of the radical concentration.

Restricted access