Conformation of polymer

Changes in the conformation of polymer chain backbone occur much more slowly in the vicinity of Tg than most of the molecular processes that serve as examples of simpler equilibria. 

Figure 9.15 Schematic illustration of size exclusion in a cylindrical pore (a) for spherical particles of radius R and (b) for a flexible chain, showing allowed (solid) and forbidden (broken) conformations of polymer.

Semiyen, J. A. Ring-Chain Equilibria and the Conformations of Polymer Chains. Vol. 21, pp. 41—75. 

Flow-induced degradation is intimately related to the nonequilibrium conformation of polymer coils and any attempt to interpret the process beyond the phenomenological stage would be incomplete without a sound understanding of chain dynamics. To make the paper self-contained and to provide a theoretical basis for the discussion, we have included some fundamental models of polymer dynamics in the next section which may also serve as a guideline for future work in the field of polymer degradation in flow. For the first-time reader, however, this section is not absolutely necessary. Further, any reader familiar with molecular rheology or interested only in experimental results can skip this section, only to go back whenever a reference is needed. 

This area of research is still at its beginning and many aspects are not resolved. This includes in particular the structure and conformation of polymers at an interface as well as the modification of polymer dynamics by the interface. We have given several examples of the potential of surface and interface analytical techniques. They provide information on surface roughness, surface composition, lateral structure, depth profiles, surface-induced order and interfacial mixing of polymers on a molecular and sometimes subnanometer scale. They thus offer a large variety of possible surface and interface studies which will help in the understanding of polymer structure and dynamics as it is modified by the influence... 

The conformation of polymer chains in an ultra-thin film has been an attractive subject in the field of polymer physics. The chain conformation has been extensively discussed theoretically and experimentally [6-11] however, the experimental technique to study an ultra-thin film is limited because it is difficult to obtain a signal from a specimen due to the low sample volume. The conformation of polymer chains in an ultra-thin film has been examined by small angle neutron scattering (SANS), and contradictory results have been reported. With decreasing film thickness, the radius of gyration, Rg, parallel to the film plane increases when the thickness is less than the unperturbed chain dimension in the bulk state [12-14]. On the other hand, Jones et al. reported that a polystyrene chain in an ultra-thin film takes a Gaussian conformation with a similar in-plane Rg to that in the bulk state [15, 16]. 

Probabilities of equilibrium conformations of polymer chains are describ-able by the Gaussian statistics. 

H2> has been used by us (1—5) and others to characterize the conformation of polymers, although it is not as sensitive to the details of polymer conformation as mK. 

Calculations on other polymers and copolymers (7) show that the NLDE is sensitive to chain length, tacticity, copolymerization, and the details of the RIS model. Thus the NLDE is potentially useful to characterize the dielectric properties, microstructures and conformations of polymers. 

The conformation of the chains of isotactic polymers in the crystalline state is generally helical and corresponds to a succession of nearly trans and gauche torsion angles, the exact values depending on the bulkiness of the side groups. Molecular mechanics calculations have been extensively used for the prediction of the chain conformation of polymers in the crystal.29... 

Cooper, D. R. and Semiyen, J. A., Equilibrium ring concentrations and the statistical conformations of polymer chains part 11. Cyclics in polyethylene terephthalate), Polymer, 14, 185 (1973). 

On the basis of the above experimental results, the expected conformations of polymer-surfactant complexes at the oil-water interface are depicted in Fig. 2.19. In case I, the added polymer associates with excess surfactants present in the bulk solution, but the complexes prefer to remain in the bulk phase. Alternately, the polymer-surfactant complexes are unable to displace the adsorbed surfactant molecules from the liquid-liquid interface. Irrespective of the amount of polymer-surfactant concentration in the bulk, the experimental decay length values remain comparable to the Debye lengths, corresponding to the concentration of ion species in the bulk solution (Eq. (2.11)). This means that the force profile is... 

Polymer reactivity can also be affected by the conformation of polymer chains [Imanishi, 1979 Overberger et al., 1973 Overberger and Morimoto, 1971 Pshezetsky et al., 1968], Whether the polymer chain exists in a tight or expanded coil can influence the accessibility of polymer functional groups and the local concentration of a small-molecule reactant. 

Dschagarowa E, Mennig G (1977) Influence of molecular weight and molecular conformation of polymers on turbulent drag reduction Rheol Acta 16 309... 

The conformation of polymers governs their various physicochemical properties. When the conformation is reversibly controlled by external stimulation, such as photons, or chemicals, the conformation change should produce a concomitant change in polymer properties in solution as well as in the gel. Polymers which change their properties reversibly by such external stimulation may be referred to as stimuli-responsive polymers. 

After the Natta s discovery of highly stereospecific polymerization processes, the interest in the preparation and properties of optically active polymers has greatly increased. In fact, the use of asymmetric catalysts or monomers to obtain optically active polymers may supply interesting informations on the mechanism of steric control in stereo-specific polymerization furthermore optical activity is an useful tool to study the polymer stereoregularity and the chain conformations of polymers in the molten state or in solution. 

---