Molekularne modele skondensowanych układów polimerowych. Krytyka rozszerzania teorii rozcieńczonych roztworów na układy sieciowe

Molecular theories of condensed polymer systems (concentrated solutions, melts, bulk polymers) have been analyzed and discussed. It has been shown that kinematics and dynamics of macromolecules in network systems (commonly recognized as appropriate models of condensed systems) are entirely different from those for isolated macromolecules in dilute solutions. Consequently, molecular theories of condensed systems can not be obtained by simple extension of dilute solution theory (e.g. the theory of Rouse or Zimm). In network systems the mobility matrices (which control viscoelastic behavior of dilute soluti ons) are indeterminate and network theories based on the modification of mobility matrices are incorrect in principle. It has been shown that viscoelastic behavior of networks with localized junctions (temporary or permanent) cannot be explained by diffusion or contact friction mechanisms because the displacement of all structural elements in the systems is, in the first approximation, affine, and the corresponding velocity difference in polymer-polymer or polymer-solvent contacts is zero. Several other mechanisms which can be responsible for viscoelasticity of networks have been discussed. It has been shown that the theory of entanglement systems can not be formulated in terms of junction positions and junction velocities alone as it had been done for isolated macromolecules and networks with localized junctions. Complete characterization of configurations in entangled systems requires (in addition to junction positions in Euclidean space) the introduction of additional variables – distances measured along the contour of macromolecular chains. Some consequences of such a formulation for viscoelastic behavior of entanglement networks have been discussed.