Nature of flexibility

Stevens, M.J., and Kremer, K. The nature of flexible linear polyelectrolytes in salt-free solution - a molecular-dynamics study. Journal of Chemical Physics, 1995, 103, No. 4, p. 1669-1690. 

Equation (2.2) reveals that r-) p is a factor of smaller than the contour length nl. Since n is large, this highlights the highly coiled nature of flexible polymer chains. 

Flexible Cellular Polymers. The application of flexible foams has been predominantly in comfort cushioning, packaging, and wearing apparel (142,170, 171), resulting in emphasis on a different set of mechanical properties than for rigid foams. The compressive nature of flexible foams (both static and dynamic) is their most significant mechanical property for most uses (Table 3). Other... 

The lamellar nature of flexible polymers crystallized from dilute solution is clearly evident in the electron micrographs given in Figs. 1-5 for trans—1,4-polybutadiene,TPBD, and trans—... 

Let us first consider very briefly the influence of various parameters (i.e., nature of flexible spacer and its length, nature and flexibility of the polymer backbone and its degree of polymerization) on the phase behavior of a side chain liquid crystalline polymer. According to some thermodynamic schemes which were described elsewhere, the increase of the degree of polymerization decreases the entropy of the system and therefore, if the monomeric structural unit exhibits a virtual or monotropic mesophase, the resulting polymer should most probably exhibit a monotropic or enantiotropic mesophase. Alternatively, if the monomeric structural unit displays an enantiotropic mesophase, the polymer should display an enantiotropic mesophase which is broader. It is also possible that the structural unit of the polymer exhibits more than one virtual mesophase and therefore, at high molecular weights the polymer will increase the number of its mesophases. All these effects were observed with various polymer systems. ... 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

Proline is relatively compact because of the cyclic nature of its side chain It has less conformational flexibility than the other ammo acids and the presence of proline affects the shape of a peptide more than other ammo acids... 

Flexible Applications. The mainstay of the lead stabilizers in the United States is in flexible wine and cable coating appHcations. The nonconductive nature of lead stabilizers is unsurpassed by other classes of stabilizers. Rather high levels of stabilizers are necessary for these uses because... 

In methacrylic ester polymers, the glass-transition temperature, is influenced primarily by the nature of the alcohol group as can be seen in Table 1. Below the the polymers are hard, brittle, and glass-like above the they are relatively soft, flexible, and mbbery. At even higher temperatures, depending on molecular weight, they flow and are tacky. Table 1 also contains typical values for the density, solubiHty parameter, and refractive index for various methacrylic homopolymers. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Although the dynamic nature of biological molecules has been well accepted for over 20 years, the extent of that flexibility, as manifested in the large structural changes that... 

From the preceding considerations it is appreciated that the intrinsic chain flexibility is determined by the nature of the chain backbone and by the nature of groups directly attached to the backbone. 

It is particularly interesting to consider the influence of the substituents R and Rj in diphenylol alkanes of the type shown in Figure 20.12. Such variations will influence properties because they affect the flexibility of the molecule about the central C-atom, the spatial symmetry of the molecule and also the interchain attraction, the three principal factors determining the physical nature of a high polymer. 

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