Polymer conformational transition

The long-standing problem of the polymer conformational transitions is an open issue of the cross-disciplinary research work and interest [1—4]. It is usually referred to as the Levinthal s paradox with an emphasis on the substantial discrepancy between the phenomenological data and the theoretical background of the issue [5]. The original Levinthal s analysis [5] has led to extensive search for the preferred pathways (trajectories) in the conformation space of a macromolecule. Recently, the problem is sharpened by the new approach that calls for the fiinnel-like form of the conformation space [6], probably offering the possibility to overcome the Levinthal s paradox. 

Chapter 10 presents an application of the two theoretical frameworks to more complex, but important systems, such as a mixture of polymers and surfactants, and network formation accompanied by polymer conformational transitions. 

Helfand E 1984. Dynamics of Conformational Transitions in Polymers. Science 226 647-650. 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

Khokhlov, A Starodybtzev, 5. and Vasilevskaya, V Conformational Transitions of Polymer Gels Theory and Experiment. Vol. 109, pp. 121-172. 

The immobilization of enzymes for sensing purposes frequently provides several important advantages an increase of its stability, operational reusability and greater efficiency in consecutive multistep reactions. Sometimes immobilization is accompanied by a certain degree of denaturalization however, the enzyme-matrix interactions may assist in stabilization preventing conformational transitions that favor such process. In some cases excessive bond formation affects the conformation of the active site and the steric hindrances caused by the polymer matrix may render an inactive sensor. 

In addition, data on the size, shape and solvation of the polymer particles in aqueous solutions at temperatures below and above the transition phenomena registered by HS-DSC have been obtained [42]. Table 2 shows the results of capillary viscometry and light scattering experiments for the fractions p and s of poly(NVCl-co-NVIAz) synthesized at 65 °C from the feed with the initial molar comonomer ratio equal to 85 15. Since fraction p precipitates from the aqueous solution at temperatures > 34 °C, its intrinsic viscosity can be determined only at 20 °C, whereas for the fraction s such measurements were possible above and below the temperatures of the HS-DSC-registered conformational transition. 

All the described properties of such a s-fraction of poly(NVCl-co-NVIAz) synthesized at the temperature above the PST of the reacting system allowed us to draw the conclusion that the chains of this type had the comonomer sequence, which at the temperatures above the conformation transition facilitated the formation of polymer particles, where H-blocks are in the interior shielded by the P-blocks against additional intermolecular association. Such a behaviour of this copolymer in aqueous media is close to that of oligomeric proteins similar to casein [46] possessing a rather hydrophobic core surrounded by the polar segments. 

The stabilization of the planar conformation in these materials is due primarily to intramolecular hydrogen bonding between the N-H and C=0 (urethane) groups on adjacent R groups. The resulting polymer conformation is shown schematically in Figure 3. This explanation of the color transition is clearly evident from infrared spectra (12), which will not be discussed here. 

The reactions of intramolecular cross-linking is a rather poorly investigated area in the field of macro-molecular reactions. However, the problems of regularities of such processes are related to such important problems of polymer chemistry as chemical modification of polymers, networks formation, sorption of low molecular reagents by polymers, intramolecular catalysis, conformational transitions and so on. In spite of the great importance of the study of regularities of cross-linking reactions, the experimental and theoretical analysis of such processes is complicated by many difficulties. ... 

Keywords. Hyperbranched macromolecules. Polymer films. Scanning force microscopy. Conformational transitions and interfacial ordering of single molecules... 

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