4. Transition temperatures. Dilatometry. Free volume

4.1 General

Plastics belonging to the various structural groups described in the previous paragraph differ in their thermal behavior.

Cooled to low temperatures, in liquid nitrogen for example, they all become rigid and brittle, in a vitreous state (by analogy with glass). But if they are gradually warmed up, various relaxation processes concerning increasingly important structural units will take place reversibly. Most of the relaxations relating to the smallest structural units will be revealed only by harmonic, electrical (see article on dielectric properties [A 3 140] ) and mechanical stresses. The latter will be discussed in conjunction with periodic dynamic tests...