Poly concentration dependence

A comparison of values of yield stress for filled polymers of the same nature but of different molecular weights is of fundamental interest. An example of experimental results very clearly answering the question about the role of molecular weight is given in Fig. 9, where the concentration dependences of yield stress are presented for two filled poly(isobutilene)s with the viscosity differing by more than 103 times. As is seen, a difference between molecular weights and, as a result, a vast difference in the viscosity of a polymer, do not affect the values of yield stress. 

Fig. 9. Concentration dependences of yield stress for low- and high-molecular poly(isobutylene)s filled by highly active carbon black...

Fig. 10. Concentration dependence of a modulus in the region of low-frequency plateau (i.e. yield stress , measured by a dynamic modulus). Dispersion medium poly (butadiene) with M = 1.35 x 105 (7), silicone oil (2) polybutadiene with M = 1 x I04 (3). The points are taken from Ref. [6], The straight line through these points is drawn by the author of the present paper. In the original work the points are connected by a curve in another manner...

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly scavenged superoxide anion in a concentration-dependent manner, and almost completely scavenged at 200 p.M of a catechin unit concentration. The laccase-catalyzed synthesized poly(catechin) also showed excellent antioxidant property. Catechin showed pro-oxidant property in concentrations lower than 300 jlM. These results demonstrated that the enzymatically synthesized poly(catechin) possessed much higher potential for superoxide anion scavenging, compared with intact catechin. 

The data in Figure 5 can now be considered in light of the conduction model developed above. As stated previously, conduction in reduced poly-I behaves like an activated process. There are two sources that potentially could be responsible for this behavior. The first is the Boltzmann type concentration dependence of the 1+ and 1- states discussed above. The number of charge carriers is expected to decrease approximately exponentially with T. The second is the activation barrier to self-exchange between 1+ and 0 sites and 0 and 1- sites. For low concentration of charge carriers both processes are expected to contribute to the measured resistance. 

If poly(U)-dependent polyphenylalanine synthesis is to be measured, the amount of template to be used is 5 fig/reaction mixture, the Mg acetate concentration is increased to 12 mM, and the amino acid mixture is omitted. 

V, is the molar volume of polymer or solvent, as appropriate, and the concentration is in mass per unit volume. It can be seen from Equation (2.42) that the interaction term changes with the square of the polymer concentration but more importantly for our discussion is the implications of the value of x- When x = 0.5 we are left with the van t Hoff expression which describes the osmotic pressure of an ideal polymer solution. A sol vent/temperature condition that yields this result is known as the 0-condition. For example, the 0-temperature for poly(styrene) in cyclohexane is 311.5 K. At this temperature, the poly(styrene) molecule is at its closest to a random coil configuration because its conformation is unperturbed by specific solvent effects. If x is greater than 0.5 we have a poor solvent for our polymer and the coil will collapse. At x values less than 0.5 we have the polymer in a good solvent and the conformation will be expanded in order to pack as many solvent molecules around each chain segment as possible. A 0-condition is often used when determining the molecular weight of a polymer by measurement of the concentration dependence of viscosity, for example, but solution polymers are invariably used in better than 0-conditions. 

In concluding this section, we should touch upon phase boundary concentration data for poly(p-benzamide) dimethylacetamide + 4% LiCl [89], poly(p-phenylene terephthalamide) (PPTA Kevlar)-sulfuric acid [90], and (hydroxy-propyl)cellulose-dichloroacetic acid solutions [91]. Although not included in Figs. 7 and 8, they show appreciable downward deviations from the prediction by the scaled particle theory for the wormlike hard spherocylinder. Arpin and Strazielle [30] found a negative concentration dependence of the reduced viscosity for PPTA in dilute Solution of sulfuric acid, as often reported on polyelectrolyte systems. Therefore, the deviation of the Ci data for PPTA in sulfuric acid from the scaled particle theory may be attributed to the electrostatic interaction. For the other two systems too, the low C] values may be due to the protonation of the polymer, because the solvents of these systems are very polar. 

Recently, experimental data of S for various liquid-crystalline polymer solutions have become available. Figure 12 illustrates the concentration dependence of S for three polymer liquid crystal systems (a) PBLG-DMF [92,93], (b) PHIC-toluene [94], and (c) poly(yne)-platinum polymer (PYPt)-trichloro-ethane (TCE) [33]. For systems (a) and (c), with the alignment made by... 

The data in Figure 1 show no dramatic concentration dependence for the interaction of either tetrahydrofuran or 2,5-dimethyltetrahydrofuran with poly(styryl)lithium. The absence of distinct breaks within the range of R values from 0.2 to 2 can be regarded as evidence that the initial base coordination process (eq 1) is followed by successive coordination with other tetrahydrofuran molecules as shown in eq 2. 

The enthalpies of coordination of tetrahydrofuran with poly(isoprenyl)lithium exhibit a dramatic concentration dependence as shown in Figure 3. The enthalpies decrease from -5.8... 

The concept of a unique hydrodynamic volume for all rodlike polymers was derived from examination of the Mark-Houwink constants, K and a, of the equation [rj ] = KMa. Macromolecules with values of a greater than unity are commonly accepted to be stiff or rigid rods. However, it was also found that such molecules (even for values of a less than unity) obey a relation illustrated by close concordance with the curve in Fig. lb (13) flexible, branched or otherwise irregular polymers, on the other hand, show dispersion around the upper part of the curve. The straight line curve in Fig. lb implies that the constants K and a are not independent parameters for the regular macromolecules to which they apply. Poly (a- and polyQJ-phenylethyl isocyanide) fall on this line the former has a value of a > 1 while the latter has a value a < 1 (14) both polymers give linear concentration dependence of reduced specific viscosity for fractionated samples... 

Fig. 6. Concentration dependences of a apparent molecular weights ", and b freezing-point depression 6 per unit concentration c in benzene of poly(a-phenylethyl isocyanide) of Mn = 34800. [Reproduced from Ref. (21), with permission of J. Wiley and Sons, Publ.]...

Fig. 10. Double extrapolation surface of viscosity time-decay and concentration dependence of poly(sec-butyl isocyanide) in dichloroacetic acid at 30° C (20)...

Fig. 11. Concentration dependence of reduced viscosities of various unfractionated samples of poly[(a-carboxymethyl)ethyl isocyanide] in 1,2-dichloroethane at 30° C (9)...

The viscosity behavior of poly[(a-carboxymethyl)ethyl isocyanide] may be studied in neutral organic solvents. The concentration dependence of its reduced specific viscosity in 1,2-dichloroethane is shown in Fig. 11. A linear dependence indicates that the coefficients of higher concentration terms of the usual virial equations are negligibly small—a case which should be found with molecules, such as stiff rods, that give few intermolecular entanglements in dilute solution. 

Fig. 8. The cross-linker concentration dependence of the friction coefficient of the poly(acrylamide) gel. The total concentration of the gel is constant at 700 mM...

Kakizaki, M. and Hideshima, T., Effect of distribution of free volume on concentration dependence of dielectric relaxation in water mixtures with poly(ethylene glycol) and glucose, Jpn. J. Appl. Phys., Part 1, 1998, 37, 900. 

This is consistent with the relative ease of dissociation of poly(styryl)lithium in the presence of bases and also with the concentration dependence of enthalpy versus R plot (Fig. 4) with a break observed at an R value of ca. 1.0. These calorimetric results are also in agreement with the stoichiometric dependencies observed by Helary and Fontanille 92> from their kinetic and spectroscopic studies. For example, they reported that the UV wavelength of maximum absorption of poly(styryl)lithium shifted upon additions of TMEDA until an R value of 1.0 and then was constant. They also observed that TMEDA additions increased or decreased the rate of polymerization, depending on [PSLi] the increase or decrease in the rate leveled off at an R value of ca. 1.0. All... 

Figure 10.9 Conformation of a linear poly electrolyte depending on salt concentration. At high salt concentration they tend to from a dense random coil which changes to a more stretched conformation at low salt concentration. In addition, the conformation in the adsorbed state is indicated.

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