Inherent structures , glass transition

Because of the angled structure of poly(arylene ether sulfone)s, they generally do not crystallize. They are thus amorphous and optically transparent with glass transition temperatures between 150-200 °C. They are soluble in some polar solvents, hydrolysis resistant, and inherently flame resistant. Fields of application for these materials are found particularly in the area of electronics and membrane technology. 

Physical data that appear in this text are taken from reliable sources, but it is not unusual to find different values in different sources for the same polymer. For example, the glass transition of polyethylene can be found listed as -128°C, -80°C, and -30°C (almost a 100°C range ), supposedly for the same material. Discrepancies such as this can arise from differences in structure between samples, either because the materials are inherently different, or because of the way the samples were prepared. In some cases, different measurement techniques give different values for the same sample. Although we will try to choose values that are representative, do not be surprised to find somewhat different values in any given source. 

For this reason one has to revise the deformation mechanism during microhardness determination commonly used for complex systems comprising components or phases with glass transition temperatures below room temperature. For this purpose it is convenient to remember again the structural peculiarity of the system under investigation. The fact that the PBT crystallites are floating in a matrix of low viscosity has important consequences on the microhardness behaviour. Because they are floating in a liquid of low viscosity, the crystallites of PBT as well as the PBT amorphous phase cannot respond to the external stress in a way that demonstrates their inherent microhardness, however, one can measure the response of the crystallites embedded in the liquid matrix. 

Fig. 10. Schematic illustration of mean-squared atomic displacements versus temperature, measured from the inherent structure, for amorphous-phase basins. The melting, MCT singular, and glass transition temperatures are Tm, T, and Eg, respectively.

Blending of poly(ethylene terephthalate) (PET) and poly (ethylene naphthalene-2,6-dicarboxylate) (PEN) has been shown to be an attractive possibility to combine the inherent economics of PET with the superior mechanical, thermal and barrier properties of PEN [24]. The molecular structure of PEN is stiffer than that of PET due to the presence in its main chain of naphthalene instead of benzene rings. The glass-transition temperature, Tg, of PEN is about 50° C higher than that of PET contributing to a better performance in terms of thermal, mechanical, and gas barrier properties [17,24]. PET and... 

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