Intrinsic viscosities trends

Conformation in solution is indicated by the way in which the hydro-dynamic properties of the macromolecules change with change in molecular weight. From trends in the intrinsic viscosity, the sedimentation coefficient, or the diffusion constant with molecular weight we can learn something about the conformation of the molecule in solution (19,20). 

Although the values of Intrinsic viscosity determined with a low shear viscometer are the only ones which truly represent the Intrinsic viscosity at high molecular weights, the results from the capillary viscometer are shown In Figure 7 to give an Indication of the effect of shear In the viscosity range of the study. The values of Intrinsic viscosity are different for the two types of viscometers, but the trend of Intrinsic viscosity versus conversion Is still the same. 

Figure 12.1. Predicted trends for the intrinsic viscosity [p] of a polymer with M=100 g/mole, K=30 g°-25,cm1-5/mole0-75 and Mcr=10000 g/mole, as a function of the viscosity-average molecular weight Mv of the polymer (for Mv>Mcr) and the quality of the solvent (and hence the value of the exponent a in Equation 12.14).

Viscosities of the copolymers were measured in Freon 113 at 35 °C (Figure 9). For copolymers of hexafluoroacetone and ethylene, the intrinsic viscosity is much higher at -78°C than at 0°C. A similar trend has been observed for the ternary system of ethylene-tetrafluoro-ethylene-hexafluoroacetone (7). 

The intrinsic viscosity [q] (ml/g) of the polysoap in the organic phase is given as a function of a in Figure 8. A marked dependence of [ti] on the nature of the ion and opposite to the trend of the thermodynamic constant (which increases in the direction Na>K>Cs, cf. Figure 5) is displayed. Qualitatively, one may say that the occurrence of intramolecular polymer-polymer bonds is greater for the ions the most in need of hydration. 

X 10. After approximately lOOh storage viscosity stability was achieved. Reduced as well as intrinsic viscosities pass obviously through a maximum with increased salt concentration. This trend is also observed in the presence of LiCl and urea. Such observations may be related to a change in intramolecular H-bonding that would be destroyed in the presence of salt or urea and to the existence of an osmotic effect at higher salt concentrations that would cause a decrease in the viscosity. 

The development ofand new trends in the determination of molecular weights and molecular weight distribution of aliphatic unsubstituted linear polyamides (nylons) are reviewed here. Critically discussed are intrinsic viscosity - molecular weight relationships and the conformational regidity of nylon chains. Attention is also given to some peculiarities in the behavior of nylons in multicomponent solvents. 

Trends in Molecular Weight and Intrinsic Viscosity during Polymer Reactions... 

The most significant drop of intrinsic viscosity takes place in the initial (15-20 min) period. Further enzymatic exposure of specimens doesn t greatly affect the degree of intrinsic viscosity drop. One can also note that both at short and at long periods of holding the films in contact with enzyme solution one and the same trend persists - the least variation of polymer molecular mass is observed in the film obtained from 1% acid while the greatest one - in the films from 10% and especially 70% AcOH (Table 1). 

Recenly, except from homopolymers, copolymers based on 1,3-propanediol, succinic acid and other diacids or diols were synthesized [34], A full series of random poly(butylene-co-propylene succinate) (PBPSu) copolymers with high molecular weight were prepared, by the polycondensation method. The intrinsic viscosity of the copolymers ranged from 0.6 up to 0.75 dL/g, but without showing any clear trend for the dependence on composition. The copolyesters showed a melting point depression with increasing comonomer content, as can be seen in Figure 10. 

The authors reported that polyamides prepared by the interfacial method had generally higher intrinsic viscosity values and slightly lower rotatory powers than those obtained by aminolysis but they concluded that the polyamides prepared by both methods had the same characteristic trends in optical properties within the limits of experimental error. 

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