Properties of Constitutive Equations for Undilute Linear Polymers Based on the Molecular Theory

The theoretical ideas of the viscoelasticity mechanism and the ways of their mathematical interpretation being developed simultaneously with the experimental studies are based on the construction of constitutive equations capable of describing the observed features of the viscoelastic behavior of a polymer system. Notwithstanding the considerable achievements of the nonstructural-phenomenological theories, it is obvious that the constitutive equations must be formulated by proceeding from principles based on the dynamics of individual macromolecules. This would enable one to relate the phenomenological constants of the theory to the specific characteristics of a macromolecular chain. The theoretical concepts of the viscoelasticity mechanism of a system of weakly coupled macromolecules have been discussed. The basic conclusions of the theory and its experimental verification bring to light the main features of the behavior of a macromolecule in an undiluted system (among other like macromolecules), namely: "to a first approximation" when perturbed a macromolecule moves in an undiluted system as in an after effect medium; the mean displacement of its center of gravity is of a monotonic and nonlinear nature, viz. the macromolecule is localized near its initial position-a scale of localization or an internal length appears.