Glass recrystallisation method

Method I.—40 gms. (1 mol.) of finely divided cinnamic acid are spread out on a large clock-glass and placed in a desiccator over concentrated sulphuric acid. A dish containing 45 gms. (slightly more than 1 mol.) of dry bromine is supported on a glass tripod above the cinnamic acid, the desiccator is closed, and allowed to stand until all the bromine has evaporated from the dish, and has been absorbed by the acid (about 3 days). The clock-glass is removed, the product exposed to the air for several hours, weighed in order to make sure that the theoretical amount of bromine has been absorbed, and recrystallised from dilute alcohol. 

Figure 1.24 Step-scan trace of PET shown as a function of time. The step increase in Cp identifies the glass transition, whilst a slight reduction also occurs as the sample recrystallises. The IsoK curve matches the lower envelope of the heat flow data. Quantitative data of these types require a baseline subtraction in accord with the requirements of the Cp method. Qualitative data showing the events can be obtained if this is not performed.

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