Polymer structure and conformation

Chemical programming of polymers has proven to be a crucial tool in mimicking virus-like features. Thus, alterations in polymer structure and conformation can be correlated to transfection efficiency and cytotoxicity. It has to be considered that the better polymer structure is defined, the more detailed study of structure-activity relationships is possible. First approaches towards better defined polymer structure with narrow molecular weight distribution have been made by PAE and pseudo-dendrimer synthesis already discussed in Sect. 4.1. 

In 1962 Dr. Bovey joined Bell Laboratories as a member of the technical staff, and was appointed to his present position in 1967. He continued his detailed studies of polymer structure and conformation at Bell Laboratories, and extended the scope of his work to include investigations of nuclei other than protons, branch analyses in polyethylene, and determination of defect structures in vinyl and related polymers. He continues to have a vigorous research program in the areas of polymer conformations in the solid state, polymer morphology, and the mechanisms of polymer stabilization and degradation. 

Several aspects of polymer thin films have thus been investigated while many others are still unexplored. These include structural and conformational aspects where polymer thin film properties are theoretically well-treated but experimental data are generally missing. However, with further development of experimental techniques this area might become accessible in the near future. 

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... 

Exchange of counter-ions (and solvent) between the polymer and the solution in order to keep the electroneutrality in the film. In a compacted or stressed film, these kinetics are under conformational relaxation control while the structure relaxes. After the initial relaxation, the polymer swells, and conformational changes continue under counter-ion diffusion control in the gel film from the solution. 

Interactions with xanthan were investigated for some GAX fractions of wheat bran [109]. Whereas, for lowly substituted GaMs a synergy in viscosity was observed at low total polymer concentrations, yielding a maximum of the relative viscosity at nearly equal proportions of both polysaccharides [124], the xanthan/xylan mixtures at the same experimental conditions showed no synergy. The observed decrease in the relative viscosity values upon addition of the xylan indicates that a certain interaction with xanthan takes place, but that it leads to a contraction in the hydrodynamic volume. The authors suggested that structural and conformational differences between GaM and GAX might be the reason for this observation. 

In order to understand polymer solution behaviour, the samples have to be characterised with respect to their molecular configuration, their molar mass and polydispersity, the polymer concentration and the shear rate. Classical techniques of polymer characterisation (light scattering, viscometry, ultracentrifugation, etc.) yield information on the solution structure and conformation of single macromolecules, as well as on the thermodynamic interactions with the solvent. In technical concentrations the behaviour of the dissolved polymer is more complicated because additional intramolecular and intermolecular interactions between polymer segments appear. 

Abstract Conjugated polymers have many unique photophysical properties that make them useful for a variety of applications within the fields of chemistry, molecular biology, and medicine, specifically their ability to produce a conformation-dependant spectral signature reflective of changes in their local environment. This physical property makes conjugated polymers an indispensible tool in the toolbox of fluorescent reporters, and within this chapter, their utilization as molecular probes for studying protein structure and conformation is emphasized. 

Studies of amino acids and peptides have been a major component of VCD research. From a biophysical standpoint, VCD provides a unique source of solution phase structural and conformational information. In addition, the previously discussed molecules have been the focus of numerous theoretical investigations. The major role of electronic currents in generating biased VCD was first recognized in interpreting amino acid VCD spectra. The polypeptide spectra have provided a test for theoretical descriptions of VCD in a-helical polymers. 

See for example (a) J. C. Randall, Polymer Sequence Determination C NMR Method, Academic Press, New York 1977, (b) E. A. Bovey, Chain Structure and Conformation of Macromolecules, Academic Press New York, 1982 (c) A. E. Tonelli, NMR Spectroscopy and Polymer Microstructure ... 

It is important to realize that polymer configuration and conformation are related. Thus, there is a great tendency for isotactic polymers (configuration) to form helical structures (conformation) in an effort to minimize steric constrains brought about because of the isotactic geometry. 

Photoresponsive polymers are quite special polymers, able to respond to light and dark conditions and thus giving rise to reversible variations in their structure and conformation. These photoinduced structural changes may in turn be accompanied by reversible changes in the physical and chemical properties of the polymeric materials. 

More specifically, conformational analysis can provide information on stable isomeric states, which are defined as minima on energy-deformation plots, and on the energy barriers between these minima. Through these minima, the population of each state at different temperatures at thermodynamic equilibrium can be determined, and a description of the kinetics of the transition from one isomeric state to another can be obtained. Therefore, conformational analysis can define chain flexibility completely. Thus, conformational analysis is the key element required to establish the conceptual bridge between polymer structure and physical properties. 

Data on the optical anisotropy and equilibrium rigidity of aromatic polymers can be used to draw conclusions on their structural and conformational properties. 

The possibility of using the Kerr effect for the study of the structure and conformation of polymer molecules greatly depends on whether it is used for solutions of flexible-chain or rigid-chain molecules ... 

The expoimental data on the non-steady state Ken effect of flexible-chain polymers dissolved in solvents with moderate viscosities reveal that at frequences up to lO Hz no dispersion of B is observed (just as in solutions of low molecular weight substances and monomers). This is also an indication of mutually independent orientation of single monomer units in the electric field which is only sightly related to the structure and conformation of the polymer chain as a whole. 

Table 8). This permits the interpretation of experimental data by using the electro-optical properties of flexible-chain polymers in terms of a worm-like chain model However, EB in solutions of polyelectrolytes is of a complex nature. The high value of the observed effect is caused by the polarization of the ionic atmosphere surrounding the ionized macromolecule rather than by the dipolar and dielectric structure of the polymer chain. This polarization induced by the electric field depends on the ionic state of the solution and the ionogenic properties of the polymer chain whereas its dependence on the chain structure and conformation is slight. Hence, the information on the optical, dipolar and conformational properties of macromoiecules obtained by using EB data in solutions of flexible-chain polyelectrolytes is usually only qualitative. Studies of the kinetics of the Kerr effect in polyelectrolytes (arried out by pulsed technique) are more useful since in these... 

When two biopolymers that differ in structure and conformation are mixed together, enthalpically favorable interactions will promote association between the two polymers but if the heterotypic interactions are enthalpically unfavorable, thermodynamic incompatibility occurs with a tendency to phase separation (Tolstoguzov, 1991). 

For a polyanUine film, the light absorption measurements were conducted after the film was exposed to HCl and NH3 vapors, respectively, as shown in Fig. 14 [19]. The difference in the spectra indicated that HCl and NH3 vapors induced a different band structure and conformation of the polymer. Therefore, the optical property of the film changed when the film switched from one state (doped by HCl) to another (dedoped by NH3). The refractive index measurement by ellipsometry showed that the refractive index changed from 2.43 (doped by HCl) to 1.95 (dedoped by NH3). 

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