The elasticity in the presence of diluents.

A review is given of the thermoelastic measurements performed om different materials. Basically, all materials can be divided into two groups. Fro crystalline and glassy materials the enthalpy component of the retractive force is large and the entropy component is small. On the other hand, for amorphous, crosslinked polymers the opposite is true. After corrections are made for volume changes, the energy component is generally small and the entropy component is large. Only rubber-like polymers, whether diluted or not, are known to display the latter behavior. Moreover, these materials generally undergo glass transitions upon cooling. In these physical properties elastin behaves like the latter class. Therefore in the absence of evidence to the contrary, elastin must be considered to be an amorphous, crosslinked polymer displaying rubberlike elasticity.