4. Determination of characteristic quantities

Starting from the molten state where the polymer is amorphous, and depending on the cooling rate, the polymer can assume two different states:

• a semi-crystalline state if cooling is slow; for this state, a crystallinity rate is defined ;

• if cooling is rapid, the polymer remains in an amorphous state and can reach the glassy state, which is also an amorphous state, without passing through the solidification phase. It is then possible to represent the variation of amorphous polymer densities as a function of temperature and pressure by a single equation throughout the experimental range.

Differential thermal analysis (DTA) has a number of advantages over PvT techniques. In particular, it enables us to work on small samples, and is well suited to measuring crystallinity rates...