Rubber Elasticity and Mean Orientation of Segments

It is impossible, apparently, to discuss the phenomena of elasticity, optical anisotropy and dielectric permittivity of polymer without referring to motion of the Kuhn s segments. Indeed, for example, from the time of classical 

Considering the entangled systems in the coarse-grained approximation, we forget about segments the theory contains the effective elastic forces between the fictious adjacent particles, and the stress tensor (equation (6.7)) can be expressed through the variables and u k in the form 

However, in this case, the stresses in entangled systems can also be related to the tensor of mean orientation of the segments with a relation similar to equation (7.45), but with other coefficient of proportionality, because we deal with non-equilibrium situation in this case. In this way one can correspond the two expressions for the stress tensor to each other and relate the introduced variables xft and u k to the tensor of mean orientation of the segments 

The relaxation of orientation of segments is intrisinsigly included in the theory from the very beginning. Indeed, in Chapter 3, discussing the main assumption of the theory, we assumed that there is an underlying relaxation process, which is described by relaxation equation (3.14), that is 

One can guess that this relaxation process describe the relaxation of mean orientation of segments with the relaxation time r. It is remarkable that for 

---