Changes in Polymer Chains

It should be noted that complex formation often allows stabilization of conformational and tautomeric forms, which are not characteristic of the parent polymers. A representative example is poly(ethylene glycol) (PEG), which has a helical structure with alternating trans- and gauche-CO, OC, and C-C bonds, respectively (T2G conformation, helix 2). PEG reacts with HgCl2 to form a complex of 

It should be noted for comparison, however, that the structural properties of PEG-alkali metal ion macrocomplexes are better described in terms of a double helix model.  

Metal ions are usually linked to a macrochain through the formation of several bonds with one (intramolecular complexes) or more (intermolecular complexes) chains. Dilute solutions prefer intramolecular complexes and concentrated solutions and matrixes provide intermolecular complexes. In intramolecular complex formation 

However, it has been found that Kj, the stability constant for the fth complex, usually increases with conversion level in contrast to the behavior of low-molecular-weight analogs (Table 1). 

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CALCULATED DIMENSIONAL CHANGES IN POLYMER CHAINS IN STRETCHED ELASTOMERS... 

Although the general picture can be drawn, several problems must be solved that arise from the interaction of polyelectrolytes (polycation and polyanion) with ions (MV2+ and EDTA). These interactions bring about changes in polymer chain configuration. This effect is manifested by the... 

Even when the azobenzene chromophores are incorporated into the polymer backbone, the dipole moment increase of azobenzene residues by photoirradiation can also induce a change in polymer chain conformation. The solution viscosity of poly(dimethylsiloxane) containing azobenzene residues in the main chain decreased upon ultraviolet irradiation, and the effect was attributed to the trans to cis photoisomerization [9]. The photodecrease of the viscosity depended on the polarity of the solvent. It was 24% in non-polar heptane, but negligible in polar dichloroethane. 

Dynatrol Viscosity Systems are designed for continuous measurement of viscosity in process streams. Dynatrol Viscosity Detectors are installed directly in process vessels without the need for sampling or analysis. Response is immediate and continuous. Utilizing this system, we carried out a series of experiments to study the change in viscosity of polymer solutions when we introduced a change in polymer chain ends. 

Schematic representation of macroconformational (left) and microconformational (right) changes in polymer chains... 

It is often important to correlate changes in polymer chain segments relative to the deformation axis in terms of the dichroic ratio. Typically, relative absorbances are measured for various functional groups. The differences represent the time-dependent reorientational rates of different structural imits. The orientation of various fimctional groups may be dependent on the magnitude and specificity of various inter- and intramolecular interactions. Therefore, the rates of orientation and relaxation provide useful information of the local chemical environment. In polystyrene, a pair of strong cross peaks can be located at the lower left... 

Hjertberg et al. ° have reported the circular dichroism (CD) spectrum of the related chiral polythiophene 30, which contains a chiral amino acid group attached to the thiophene units by an ether linkage. In water solvent, a pair of exciton-coupled CD bands are observed in the visible region associated with the k-k transition band in the UV-visible spectrum at ca. 430 nm. These chiroptical features are attributed to a helical conformation adopted by the polymer backbone under the influence of the chiral side chain. However, in methanol solvent no CD bands are observed and the tt-tt absorption band is blue shifted. This suggests a change in polymer chain conformation in methanol solvent to a more planar arrangement. 

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