Molecular poly

The variations in the value of molecular weight may be due to the poly-molecularity of the samples and to inadvertent degradation during isolation. 

In the preceding publication (I), five replications for the cellulose II sample were tabulated in Figure 3 to show that variations in DPn were noted when the related DPW data were in good agreement. The poly-molecularity ratios for the DP values fluctuate widely as a consequence of this. These results are compared in Table IV with those now obtained from the same data. The improvement in the values is quite marked as the statistical analysis of the data indicates. 

These results are confirmed by Soviet work which studied the effect of velocity and temperature upon the eutectic mixture MBBA, EBBA with a of 52 C and compared their results with the lubrication of "MS 20 aviation oil". Lubrication by LC reduced the friction coefficient to one-fifth of that of the oil (Fig. 22a). In ref 9 LC is compared to vaseline oil with the same result. (Fig. 22b). In all these experiments,vi is lower than 0.05 which indicates the presence of a poly molecular layer of lubricant. 

Fig. 6 gives an example, from which may be concluded that with the sol concentration chosen, the five different kinds of "particles used as "electrophoretic indicators are covered with a complete colloid film. To avoid misinterpretation we must add that the adjective "complete does not give any information on the structure of the colloid film formed. Thus complete does not mean, for instance that a monomolecular colloid film on the particle surface would have been completed. It only means that the mono- di- or perhaps poly-molecular colloid film formed possesses such a boundary with the surrounding sol, that its electrophoretic properties have become independent of those of the original particle surface. 

The ratio A//A/ is called polydispersity (the previously used term was poly-molecularity) of a polymer and it gives important information on the width of its molar mass dispersity. Less frequently, the viscosity average molar mass, A/, and the artificial z and z+1 averages of molar mass. A/ and Af are considered. M is defined... 

Figure 3.14. Simulated CPC of the F+LMWL system where the polymer has the same p, with different poly-molecularity (sp is the spinodal, eir-cles are the critical points, u) o ifu present hypothetical mixtures of two polymers with the exponential MWD) (Koniiigsveld, 1968) [Reprinted from Advances in ( olloid and Interface Science 2 (1968) 151-215. ( opyright 1968 with kind permis-.sion of Elsevier Science NL, Sara Ourgerhart-...

Van t Hoff classified chemical reactions at microscopic level as mono-bi and poly molecular processes, interpreting the polymolecular processes from their stoichiometry as a sequence of mono and/or bimolecular steps. From these conclusions and the equation (12) Arrhenius will get the basis for his studies. 

The data in Fig. 4 refer to linear polyethylene samples with less broad distributions since they were obtained by fractionation of a commercial Marlex 50 type polyethylene into 10 fractions. The shape of the curves indicates that some of them would intersect, if extrapolated. This points to considerable residual poly-molecularity in the fractions so that identification of minima with critical points is not permitted. Nakajima et al. [35, 36] nevertheless analyzed the data assuming the identification to be allowed and, using the Shultz-Flory method [45], derived values for the critical temperatures for solutions of polyethylene of infinite molar mass in -alkanes. This specific temperature is known as the theta temperature, . Nakajima et al. s values, listed in Table 4, agree within 5 K with those... 

The general physical properties are as a rule independent of whether the particles are mono- or poly-molecular on the other hand they will often be found dependent to a high degree on the shape of the. particles, discussed in the previous paragraph ... 

Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70.

A great many polymers appear to form films having a flat molecular configuration. Thus various polyesters [7] gave extrapolated areas of about 2.5 m /mg corresponding to about the calculated 60-70 area per segment, or mono-layer Sickness of 3-5 A. A similar behavior was noted for poly(vinyl acetate)... 

The analogous coupling between the antisyimnetric stretch and bend is forbidden in the H2O Hamiltonian because of syimnetry.) The 2 1 resonance is known as a Femii resonance after its introduction [ ] in molecular spectroscopy. The 2 1 resonance is often very prominent in spectra, especially between stretch and bend modes, which often have approximate 2 1 frequency ratios. The 2 1 couplmg leaves unchanged as a poly ad number the sum ... 

A graphical method, proposed by Zimm (thus tenned the Zinnn plot), can be used to perfomi this double extrapolation to detemiine the molecular weight, the radius of gyration and the second virial coefficient. An example of a Zinnn plot is shown in figure Bl.9.6 where the light scattering data from a solution of poly... 

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

Figure C2.1.8. Reduced osmotic pressure V l(RTc as a function of the polymer weight concentration for solutions of poly(a-metliylstyrene) in toluene at 25 °C. The molecular weight of poly(a-metliylstyrene) varies...

A polymer is a macromolecule that is constructed by chemically linking together a sequent of molecular fragments. In simple synthetic polymers such as polyethylene or polystyrer all of the molecular fragments comprise the same basic unit (or monomer). Other poly me contain mixtures of monomers. Proteins, for example, are polypeptide chains in which eac unit is one of the twenty amino acids. Cross-linking between different chains gives rise to j-further variations in the constitution and structure of a polymer. All of these features me affect the overall properties of the molecule, sometimes in a dramatic way. Moreover, or... 

Mono- and di saccharides are colourless solids or sjrrupy liquids, which are freely soluble in water, practically insoluble in ether and other organic solvents, and neutral in reaction. Polysaccharides possess similar properties, but are generally insoluble in water because of their high molecular weights. Both poly- and di-saccharides are converted into monosaccharides upon hydrolysis. 

At 25°C, the Mark-Houwink exponent for poly(methyl methacrylate) has the value 0.69 in acetone and 0.83 in chloroform. Calculate (retaining more significant figures than strictly warranted) the value of that would be obtained for a sample with the following molecular weight distribution if the sample were studied by viscometry in each of these solvents ... 

As we did in the case of relaxation, we now compare the behavior predicted by the Voigt model—and, for that matter, the Maxwell model—with the behavior of actual polymer samples in a creep experiment. Figure 3.12 shows plots of such experiments for two polymers. The graph is on log-log coordinates and should therefore be compared with Fig. 3.11b. The polymers are polystyrene of molecular weight 6.0 X 10 at a reduced temperature of 100°C and cis-poly-isoprene of molecular weight 6.2 X 10 at a reduced temperature of -30°C. 

Figure 3.16 Some experimental dynamic components, (a) Storage and loss compliance of crystalline polytetrafluoroethylene measured at different frequencies. [Data from E. R. Fitzgerald, J. Chem. Phys. 27 1 180 (1957).] (b) Storage modulus and loss tangent of poly(methyl acrylate) and poly(methyl methacrylate) measured at different temperatures. (Reprinted with permission from J. Heijboer in D. J. Meier (Ed.), Molecular Basis of Transitions and Relaxations, Gordon and Breach, New York, 1978.)...

It is not the purpose of this book to discuss in detail the contributions of NMR spectroscopy to the determination of molecular structure. This is a specialized field in itself and a great deal has been written on the subject. In this section we shall consider only the application of NMR to the elucidation of stereoregularity in polymers. Numerous other applications of this powerful technique have also been made in polymer chemistry, including the study of positional and geometrical isomerism (Sec. 1.6), copolymers (Sec. 7.7), and helix-coil transitions (Sec. 1.11). We shall also make no attempt to compare the NMR spectra of various different polymers instead, we shall examine only the NMR spectra of different poly (methyl methacrylate) preparations to illustrate the capabilities of the method, using the first system that was investigated by this technique as the example. 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

If the poorer solvent is added incrementally to a system which is poly-disperse with respect to molecular weight, the phase separation affects molecules of larger n, while shorter chains are more uniformly distributed. These ideas constitute the basis for one method of polymer fractionation. We shall develop this topic in more detail in the next section. 

The solute molecular weight enters the van t Hoff equation as the factor of proportionality between the number of solute particles that the osmotic pressure counts and the mass of solute which is known from the preparation of the solution. The molecular weight that is obtained from measurements on poly disperse systems is a number average quantity. 

We shall be interested in determining the effect of electrolytes of low molecular weight on the osmotic properties of these polymer solutions. To further simplify the discussion, we shall not attempt to formulate the relationships of this section in general terms for electrolytes of different charge types-2 l, 2 2, 3 1, 3 2, and so on-but shall consider the added electrolyte to be of the 1 1 type. We also assume that these electrolytes have no effect on the state of charge of the polymer itself that is, for a polymer such as, say, poly (vinyl pyridine) in aqueous HCl or NaOH, the state of charge would depend on the pH through the water equilibrium and the reaction... 

Table 9.3 lists the intrinsic viscosity for a number of poly(caprolactam) samples of different molecular weight. The M values listed are number average figures based on both end group analysis and osmotic pressure experiments. Tlie values of [r ] were measured in w-cresol at 25°C. In the following example we consider the evaluation of the Mark-Houwink coefficients from these data. 

Table 9.3 Intrinsic Viscosity as a Function of Molecular Weight for Samples of Poly(caprolactam) ...

The intrinsic viscosity of poly(7-benzyl-L-glutamate) (Mq = 219) shows such a strong molecular weight dependence in dimethyl formamide that the polymer was suspected to exist as a helix which approximates a prolate ellipsoid of revolution in its hydrodynamic behaviorf ... 

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