Polymer continued flexibility

Figure 11.3 Schematic drawings of a worm-like polymer chain (with continuous flexibility) and a Kuhn chain (with rigid links joined at hinges that allow free rotation about the angle between the links). The length of the links has been chosen so that the contour length and mean-square end-to-end length of the Kuhn chain are the same as those of the worm-like chain. (From Donald and Windle 1992, with permission from Cambridge University Press.)...

Because a latex polymer is insoluble in water, the factors affecting the viscosity of latexes differ significantly from polymers dissolved in solvents. Since the aqueous continuous phase interacts with the polymer only at the surface of the latex particle, the molecular stracture of the polymer does not have the effect that it would if the polymer were dissolved in the liquid. The molar mass and polymer backbone flexibility, in particular, have no direct effect on the viscosity of the latex. The principal latex parameter that influences latex viscosity is of course... 

This polymer is composed of a chain of organic units joined by urethane links. Most of the PUs are thermosetting polymers, which do not melt upon heating. PUs can outperform many other polymers in flexibility, tear resistance, and abrasion resistance. This is because many devices that are used in these areas can rub against other materials and bend repeatedly. Without PUs, the continued rubbing and bending could result in the device... 

The use of polymers in medicine is steadily growing. The synthetic and processing flexibility of polymers continue to permit polymers to be applied in a broad range of medical, biological, and implant applications. Creative polymer synthesis continues to expand the functionality and tunability of polymers for medical applications. There are now excellent biomedical polymers available to address general needs in medidne (the subject of this chapter). Opportunities that present themselves for enhanced or improved biomedical polymers are in the following areas ... 

General Characterization Studies.—The continuing importance of dilute solution studies of the hydrodynamic properties of polymers is manifest in the substantial number of publications which have appeared. A summary of the more important parameters, in particular the constants in the Mark-Houwink equation [7 = KM", is presented in Table 1 for polymers with flexible chains. ... 

The freely jointed chain model is one way of describing polymers. An alternative is the worm-like chain (WLC) model [1331]. The worm-like chain model takes the polymer as an isotropic rod that is continuously flexible (Figure 11.3) this is in contrast to the freely jointed chain model that is flexible only between discrete segments. The worm-like chain model is particularly suited for describing stiffer polymers, with successive segments displaying a sort of cooperativity. A prominent example is double-stranded DNA in aqueous solution. If we stretch a worm-like chain, the force can be described by [1325, 1332, 1333]... 

The WLC model entirely neglects any discrete stmcture along the chain and describes the polymer as a continuous flexible string of constant bending module The charac-... 

Even in the absence of flow, a polymer molecule in solution is in a state of continual motion set forth by the thermal energy of the system. Rotation around any single bond of the backbone in a flexible polymer chain will induce a change in conformation. For a polyethylene molecule having (n + 1) methylene groups connected by n C — C links, the total number of available conformations increases as 3°. With the number n encompassing the range of 105 and beyond, the number of accessible conformations becomes enormous and the shape of the polymers can only be usefully described statistically. 

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