Since the results of this gas counting is directly dependent on the average length of time the sample spends in the counter as the mixed gas stream moves through it, a total integrated
A series of polycarbonates with stilbene mesogens has been prepared and characterized, expanding upon past work with stilbene-based polyesters and polyethers. It has been found that the stilbene mesogen. mono-or di-substituted with methyl or ethyl groups, significantly affects polymer morphology. Polycarbonates containing stilbene mesogens have been studied by differential calorimetry. polarized microscopy and X-ray diffraction. Methyl substituted stilbenes are semicrystalline and appear to be liquid crystalline, whereas ethyl substituted stilbenes are amorphous. Disubstitution lowers the transition temperatures from those values observed for monosubstituted stilbenes.
synopsisScreening studies have shown that of a series of halogenated vinyl polymers, poly-(vinylidine fluoride) gives comparatively good thermal protection when exposed to the intense light energy of the carbon arc-image furnace. Results indicate that this protection is undoubtedly provided by polyenes, -(CH=CF),,-, formed during pyrolysis. Decomposition products containing these structures are expelled by the gases formed into the region between the light source and the target where they intercept photons from about 200 to 500 m p and dissipate the energy to the air as heat and/or reradiate it. Instrumental evidence for polyene formation is given. The concept of polyene formation clarifies the relative thermal protection offered by a series of vinyl polymers.
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