Characterization of polysiloxanes by high-resolution pyrolysis-gas chromatography-mass spectrometry

Summary Thermal degradation of various polysiloxanes was studied by pyrolysis-gas chromatography with a fused silica capillary column. The peak identification was carried out by a directly coupled gas chromatography-mass spectrometry system. Generally, polysiloxanes were thermally degraded to cyclic oligomers along with a small amount of the compounds formed through elimination and/or recombination of the pendent substituents. Most of the degradation products including possible stereo- and structural isomers were completely separated in the high-resolution pyrograms which reflect the original stereoregularities and sequence distributions in the polysiloxane chains. Furthermore, relative peak intensities of the characteristic cyclic oligomers observed were successfully interpreted in terms of the compositions of some kinds of siloxane copolymers.

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Charakterisierung von Polysiloxanen durch hochauflösende Pyrolyse-GC-MS

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Relaxation phenomena in concentrated polyelectrolyte solution. II

Dynamic viscoelastic properties of 10 and 20% aqueous solutions of sodium polyacrylate were studied by the electromagnetic transducer method at 500 cps in the temperature range of 0–50°C. These solutions distinctly showed a relaxation phenomenon in this temperature range which was also affected by addition of such compounds as sodium chloride, urea, and dioxane. An anomalous behavior that cannot be explained as due to the relaxation phenomenon was observed on the addition of small amounts of these agents. One of the causes of this behavior is ascribed to the ion association in the solution. The static viscosity of the solution was also measured by using a rotating cylinder viscometer and the results compared with the dynamic data.     

Selenocarboxamides as new reagents for stereospecific deoxygenation of epoxides under mild conditions

Selenocarboxamides have been found to be efficient reagents for converting epoxides into olefins stereospecifically in high yields under mild conditions.     

Hadronic decay of τ

We present predictions for invariant mass distributions of the pions in τ→ν+2π and τ→ν+4π as well as improved predictions for hadronic decay rates of τ. We discuss a number of predictions which, if contradicted by τ decays, will imply the existence of a new weak interaction.     

Characterization of {v μ+1 + 2v μ,v μ + 2v μ − 1;t,q}-min · hypers and its applications to error-correcting codes

Recently, Hamada [5] characterized all {v ₂ + 2v ₁,v ₁ + 2v ₀;t,q}-min · hypers for any integert 2 and any prime powerq 3 wherev _l = (q ^l – 1)/(q – 1) for any integerl 0. The purpose of this paper is to characterize all {v _{+ 1} + 2v ,v + 2v _{– 1};t,q}-min · hypers for any integerst, and any prime powerq such thatt 3, 2 t – 1 andq 5 and to characterize all (n, k, d; q)-codes meeting the Griesmer bound (1.1) for the casek 3, d = q ^k-1 – (2q ^-1 +q ) andq 5 using the results in Hamada [3, 4, 5].     

Development of a novel solid-phase extraction element for thermal desorption gas chromatography analysis

A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%.