Glass-liquid transition and secondary transitions

The same situation prevails for PLCs. Depending on their chemical structure, semicrystalline states may or may not be obtained. However, owing to the occurrence for these polymers of nematic and/or smectic phases, either the whole material or only the non-crystalline parts of the material will yield an ordered glassy state characterized by a glass transition temperature, Tg (ordered). Such a situation is achieved by cooling the polymer slowly from the high-temperature isotropic state. Of course, if no orientation procedure has been applied, a multidomain sample is obtained. 

At temperatures below the glass transition (a), most polymers in the solid state exhibit secondary transitions (jS, y, etc.) which correspond to the motions of groups in the side chain or the main chain, such as the jS transition observed in polyacrylates or polymethacrylates assigned to the 

Finally, it follows from these considerations that in studies of molecular processes involved in the glass transition of the ordered, glassy state using a spectroscopic technique operating at a frequency /, it is essential that the mesophase found in the glassy state remains till a temperature higher than Tg(/). Typically, to perform such a study at 10 Hz it is necessary that the polymer does not undergo any mesophase transition at a temperature lower than Tg(calorimetry) + 50°C (at 10 Hz, it would be Tg (calorimetry) -h 80°C). 

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