Polymers, dynamic, definition

In the course of investigation of polymer dynamics, all topological states of chains are equivalent due to the presence of their free ends and it is not necessary to construct the topological invariant. However, for every instantaneous chain configuration, its topological state is definite and is determined by the topological invariant - the primitive path. 

Application of the considerations above to polymer chemistry leads to the definition of constitutionally dynamic polymers, dynamers, of both molecular and supramolecular types (Fig. 1) [29-32]. They behave as dynamic combinatorial entities, based on dynamic libraries whose constituents have a combinatorial diversity determined by the number of different monomers. The components incorporated by polyassociation or by polycondensation into the supramolecular or molecular polymer chains depend on the nature of the connections (recognition patterns or functional groups) and core groups, as well as on the interactions with the environment, so that dynamers possess the capacity of adaptation by association/growth/ dissociation sequences. 

The elastic and viscoelastic properties of materials are less familiar in chemistry than many other physical properties hence it is necessary to spend a fair amount of time describing the experiments and the observed response of the polymer. There are a large number of possible modes of deformation that might be considered We shall consider only elongation and shear. For each of these we consider the stress associated with a unit strain and the strain associated with a unit stress the former is called the modulus, the latter the compliance. Experiments can be time independent (equilibrium), time dependent (transient), or periodic (dynamic). Just to define and describe these basic combinations takes us into a fair amount of detail and affords some possibilities for confusion. Pay close attention to the definitions of terms and symbols. 

Ziabicki,A., Takserman-Krozer.R. General dynamic theory of macromolecular networks. I. Definitions and classification. J. Polymer Sci. Part A-2 7,2005-2018 (1969). 

In many investigations dynamic-mechanical properties have been determined not so much to correlate mechanical properties as to study the influence of polymer structure on thermo-mechanical behaviour. For this purpose, complex moduli are determined as a function of temperature at a constant frequency. In every transition region (see Chap. 2) there is a certain fall of the moduli, in many cases accompanied by a definite peak of the loss tangent (Fig. 13.22). These phenomena are called dynamic transitions. The spectrum of these damping peaks is a characteristic fingerprint of a polymer. Fig. 13.23 shows this for a series of polymers. 

The discussion in the Introduction led to the convincing assumption that the strain-dependent behavior of filled rubbers is due to the break-down of filler networks within the rubber matrix. This conviction will be enhanced in the following sections. However, in contrast to this mechanism, sometimes alternative models have been proposed. Gui et al. theorized that the strain amplitude effect was due to deformation, flow and alignment of the rubber molecules attached to the filler particle [41 ]. Another concept has been developed by Smith [42]. He has indicated that a shell of hard rubber (bound rubber) of definite thickness surrounds the filler and the non-linearity in dynamic mechanical behavior is related to the desorption and reabsorption of the hard absorbed shell around the carbon black. In a similar way, recently Maier and Goritz suggested a Langmuir-type polymer chain adsorption on the filler surface to explain the Payne-effect [43]. 

The membrane in a broad sense is a thin layer that separates two distinctively different phases, i.e., gas/gas, gas/liquid, or liquid/liquid. No characteristic requirement, such as polymer, solid, etc., applies to the nature of materials that function as a membrane. A liquid or a dynamically formed interface could also function as a membrane. Although the selective transport through a membrane is an important feature of membranes, it is not necessarily included in the broad definition of the membrane. The overall transport characteristics of a membrane depends on both the transport characteristics of the bulk phase of membrane and the interfacial characteristics between the bulk phase and the contacting phase or phases, including the concentration polarization at the interface. The term membrane is preferentially used for high-throughput membranes, and membranes with very low throughput are often expressed by the term barrier. ... 

This aspect facilitates a deeper insight into the mechanism of the Tg reductions observed in thin polymer films [36-42], Faster dynamics, by definition an increase of the average relaxation rate, can be achieved in two ways Either the polymer segments (at the molecular level), are relaxing faster... 

N.R. Prokopchuk Definition of activation energy of polymer destruction according to the data of dynamic thermogravimetry. Plastic masses (1983), No 10, 24-25 (in Russian). 

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