Interpenetration of polymers

Figure 3. (a) Conformation and coil interpenetration of polymer chains at the... 

Polymers interpenetration of polymer chains, phase separation, compatibility between polymers, interdiffusion of latex particles, interface thickness in blends of polymers, light-harvesting polymers, etc. 

FIGURE 22.2 Schematic representation of interpenetration of polymer chains and mucin glycoproteins. 

On the other hand, the increase of concentration of the polymer components leads to the suppression of the dissociation of the polyelectrolyte components due to the rise in the electrostatic repulsion within inter- and intramacromolecules and to the interpenetration of polymer chains. 

Even in the phase separated blends, where some degree of partial miscibility or compatibility exists between the components, simple melt blending in an intensive shear mixer is adequate for making a well dispersed, reasonably stable blend product with useful combination of properties, such as polypropylene/ethylene-propyl-ene rubber blend, ABS/polycarbonate blend, etc. The self-compatibUizing nature of these blends stems from partial miscibility and the mutual interpenetration of polymer chains at the interface. Slight modifications of the polymer backbone are often employed, particularly in the case of styrenic and ABS resins to induce partial miscibility with other resins. 

Chemical evidence against the interpenetration of polymer chains... 

Many problems in the physics and chemistry of polymers have been investigated by means of fluorescence techniques. Within the scope of this book, it is merely possible to point out the high versatility of these techniques rather than to discuss the innumerable publications. Among the features of luminescence that account for the variety of its applications is the fact that emission spectra can be recorded at extremely low chromophore concentrations. Thus, a polymer may be labeled with such a small amount of luminophore that the labeling does not perturb the properties of the system. As regards linear polymers in solution, it is possible to derive information on the conformational state and the behavior of the macromolecules. This concerns such topics as the interpenetration of polymer chains, the microheterogeneity of polymer solutions, conformational transitions of polymer chains, and the structures of polymer associates. Relevant work has been reviewed by Morawetz [59]. Here, only one typical example is described, which concerns the kinetics of HCl transfer from aromatic amino moieties to much more basic aliphatic amino groups attached to discrete macromolecules, in this case poly(methyl methacrylate)s (see Scheme 1.5). 

For a system with a sharp interface and weak intermolecular interaction, as in the nonpolar-polar polymer system mentioned above, failure exactly at the interface is a distinct possibility (or even probability). Thus, interfacial separation may be expected when interfadal strength is weaker than the bulk strength of the bonded materials. As we have seen, if the intermolecular interactions across the interface are more specific (including chemical bond formation) or if significant interpenetration of polymer chains occurs, rupture at the interface becomes less likely. In some cases, the locus of failure may depend on the rate at which stress is applied rapid application leads to cohesive failure and very slow apphcation, tending more toward true adhesive failure (since slow application of stress gives more time for the entangled molecules to slide past one another). 

Beyond the screening length the volume exclusions have been completely screened out due to the interpenetration of polymer coils. Therefore, the chain can be regarded as an unperturbed coil formed by blobs with the unit size and then... 

Near the theta point, the osmotic pressure of the dilute solution is closely related to the chain length of polymers, as demonstrated in (4.43). In semi-dilute solutions, however, the osmotic pressure is related to the degree of interpenetration of polymer coils, no longer related to the chain length. Using the blob model, we have... 

In concentrated solutions, with the increase of the polymer concentration, the screen effect of hydrodynamic interactions is enhanced due to the interpenetration of polymer chains. We can assume that the hydrodynamic screening length is close to the screening length of volume exclusion of monomers as given by... 

In contrast, beyond each blob, the motion range of monomers is larger than where the conditions for the free-draining mode are restored due to the interpenetration of polymer chains. Therefore, the Rouse model is applicable. 

A notion of enthalpic (AH), entropic (AS) and mixed (enthalpy-entropic) stabilization at interpenetration of polymer chains has been described. The mixing energy is... 

Figure 1.2 Schematic representation of the repulsive forces giving rise to steric stabilisation. Top shows interpenetration of polymer layers giving rise to an increase in osmotic pressure in the overlap region and bottom shows compression of the polymer layers on close approach leading to a loss of configurational entropy.

In Simha s early model (Simha and Zakin 1962), transition from a dilute to a concentrated polymer solution was envisioned as being due to interpenetration of polymer chains that occurs when concentration lies somewhere in the region 1 < [ryjc < 10. This transition is evident from the change in the concentration dependence of viscosity in polymer solutions. The quantity [r ]c, the Simha-Frisch parameter (Frisch and Simha 1956), also sometimes called the Berry number (Gupta et al. 2005), is therefore a reasonable measure of chain overiap in solution. As Shenoy et al. (2005b), however, correctly point out, the dependency, being ultimately based on the equivalent hard sphere hydrodynamic model, is strictly applicable only at low polymer concentrations. 

It is sometimes easy to overlook the fact that molecular diffusion and interpenetration can occur during the formation of adhesive bonds. Adhesives, by themselves or in combination with carrier solvents, can have a solvating effect on the surface of plastic parts. This in turn allows interpenetration of polymer molecules and may lead to bonds of exceptional durability. 

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