Polymer studies conformational change

No.19,21st Sept.1999, p.6307-18 TWO-DIMENSIONAL FOURIER TRANSFORM RAMAN CORRELATION SPECTROSCOPY STUDIES OF POLYMER BLENDS CONFORMATIONAL CHANGES AND SPECIFIC INTERACTIONS IN BLENDS OF ATACTIC POLYSTYRENE AND POLY(2,6-DIMETHYL-l,4-PHENYLENE ETHER)... 

The first term is introduced to study conformational change of polymer chains. It is written as... 

Leal LG (1986) In Rabin Y (ed) Studies of flow-induced conformation changes in dilute polymer solutions, Proceedings of the 1985 La Jolla Institute Workshop, Academic International Press, New York, p 5... 

Most descriptions of the dynamics of molecular or particle motion in solution require a knowledge of the frictional properties of the system. This is especially true for polymer solutions, colloidal suspensions, molecular transport processes, and biomolecular conformational changes. Particle friction also plays an important role in the calculation of diffusion-influenced reaction rates, which will be discussed later. Solvent multiparticle collision dynamics, in conjunction with molecular dynamics of solute particles, provides a means to study such systems. In this section we show how the frictional properties and hydrodynamic interactions among solute or colloidal particles can be studied using hybrid MPC-MD schemes. 

The recent interest in substituted silane polymers has resulted in a number of theoretical (15-19) and spectroscopic (19-21) studies. Most of the theoretical studies have assumed an all-trans planar zig-zag backbone conformation for computational simplicity. However, early PES studies of a number of short chain silicon catenates strongly suggested that the electronic properties may also depend on the conformation of the silicon backbone (22). This was recently confirmed by spectroscopic studies of poly(di-n-hexylsilane) in the solid state (23-26). Complementary studies in solution have suggested that conformational changes in the polysilane backbone may also be responsible for the unusual thermochromic behavior of many derivatives (27,28). In order to avoid the additional complexities associated with this thermochromism and possible aggregation effects at low temperatures, we have limited this report to polymer solutions at room temperature. 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

A popular theory with azo materials is that their degradation products are always aromatic amines, like azo dyes. Ueda and co-workers observed that the azo bonds in segmented polyurethenes were reduced to hydrazo intermediates after incubation with human feces, since no decrease in the molecular weight was observed [73]. It was then theorized that drug release from pellets coated with these azo polymers was due to both a conformational change and a breakdown of the film structure. Other studies also concluded that the polymers were reduced to hydrazo intermediates or were completely degraded to aromatic amines depending upon their hydrophilic/ hydrophobic nature. 

In recent years, C-NMR spectroscopy has found extensive use in studies on carbohydrate polymers, in some series overshadowing the importance of H-NMR spectroscopy. Applications range through determination of primary structure, analysis of mixtures, monitoring of chemical and enzymic transformations or of chelation reactions, and studies on conformational change. Measurements of coupling are utilized in determining the... 

It is thus expected that the conformation of the polymer-ligand chain will influence the reactivity of a metal complex. The influence of the conformational change of a poly(N-vinyl-2-methylimidazole)(PVMI 3) ligand has been studied in the electron-transfer reaction of a Co(III) complex in aqueous-alcoholic solvents87. ... 

Allosteric effects play a major role in biology, for instance in the conformational changes induced by the binding of an effector and regulating the activity of an enzyme [9.14a] they have also been studied in synthetic receptors [8.201, 8.211, 9.14b, c]. Similarly, cooperativity, a thermodynamically well defined process [9.15a], is displayed by a number of biological species as well as by abiotic ones [8.70a, 8.201, 9.15b-d] (see also Section 9.3.1, [9.64, 9.65]), in particular in organized media such as polymer solutions or gels [7.8cd, 8.290, 8.292]. 

The soluble polythiophenes are the first conducting polymers that can be taken above their glass transition without decomposition and it will be interesting to study morphology-property relationships. Heeger et al.262) have recently described conformational changes in solutions of poly-3-hexylthiophene which seem to involve a coil-helix transformation as the temperature is decreased or a poor solvent is added. 

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