CONSTRAINED EQUILIBRIUM IN NETWORK-LIKE POLYMER SYSTEMS - A CONCEPT OF IRREVERSIBLE THERMODYNAMICS

Network-like polymer systems are considered to be composed of thermodynamically equivalent subsystems. On deformation up to large strains, the shape of these subsystems is believed to be transformed according to the law of affinity. The thermodynamics of such systems is presented. This description is then extended so as to be able to describe relaxation processes. Special attention is directed to a discussion of constrained equilibrium states because of their being representative of many polymer systems. The methods of classical thermodynamics of irreversible processes are shown to be appropriate for describing large deformations of many different network-like systems such as polymer glasses and semicrystalline polymers. For the deformation experiments discussed here, the whole energy balance during deformation is known from stretching calorimetric measurements. This is a significant presumption for obtaining clear, fundamental conclusions; they would be difficult to achieve otherwise.