Volume 13, Issue 5, 01 May 1945
Index of content:
13(1945); http://dx.doi.org/10.1063/1.1724016View Description Hide Description
The determination of the molecular weights of large molecules by measuring the turbidity of the solution and the change in index of refraction with concentration is discussed. The apparatus, its calibration, and the technique used are treated together with a comparison between molecular weights measured by this method and other methods. The effect of polymolecularity is also presented.
13(1945); http://dx.doi.org/10.1063/1.1724017View Description Hide Description
The absorptionspectrum of aniline vapor has been photographed in the first and second order of a 3‐m gratingspectrograph. The strongest bands appeared as doublets and on the basis of these, a tentative analysis was made and compared with the available Raman data.
The Thermodynamics of High‐Polymer Solutions: I. The Free Energy of Mixing of Solvents and Polymers of Heterogeneous Distribution13(1945); http://dx.doi.org/10.1063/1.1724018View Description Hide Description
The theories of Flory and Huggins for the free energy of mixing of a homogeneous chain polymer of uniform molecular weight with a single uniform solvent have been extended to the case of a polymer mixture of varying chain lengths with a mixture of solvents. By making the similar assumptions as those of Huggins, and utilizing familiar statistical mechanical methods, the partial molal free energy of mixing of the solvent is found to bewhere φ0 is the volume fraction of solvent,m̄N a simple function of the number average molecular weight, and μ a constant characteristic of the polymer‐solvent mixture (consisting largely of a heat term, but also including γ, the coordination number of the rubber segments). By assuming that a mixture of two solvents behaves like a new homogeneous liquid a method of calculating μ for such mixtures is developed. Applications of these formulas to solubility and fractionation are shown in a subsequent article.
The Thermodynamics of High‐Polymer Solutions: II. The Solubility and Fractionation of a Polymer of Heterogeneous Distribution13(1945); http://dx.doi.org/10.1063/1.1724019View Description Hide Description
The free energy relations for heterogeneous molecular weight distributions developed in Part I, are applied to problems of solubility and fractionation. Critical conditions for solubility are obtained. A rigorous expression for the solubility is derived, although certain approximations are made to facilitate calculation, and to permit extension to polymers which are part ``gel.'' Following the same methods the thermodynamic equilibria involved in fractionation are described by mathematical expressions which permit a comparison of the extraction and precipitation methods. The effectiveness of fractionation is shown to be strongly dependent upon concentration.
The Influence of Molecular Flexibility on the Intrinsic Viscosity, Sedimentation, and Diffusion of High Polymers13(1945); http://dx.doi.org/10.1063/1.1724020View Description Hide Description
Expressions for the mean square separation of chain ends and modifications of the formula for an ideal coil are discussed. On the basis of these and of the hydrodynamic theory of intrinsic viscosity, an interpretation of the modified Staudinger rule is offered. It relates the exponent a of the molecular weight to a flexibility parameter p of the chain in a given solvent, varying between zero and one (Eq. (4), (5)). Recent data on polystyrene and on cellulose nitrate are analyzed in greater detail. By means of the frictional ratio f/f 0, the sedimentation constant s and the diffusion constant D, respectively, are connected with the degree of polymerization in terms of p (Eq. (9)). The limiting dependence of sedimentation and diffusion rate upon molecular weight for a straight chain and an ideal coil is also found in this manner. A comparison shows satisfactory agreement between values for p found from intrinsic viscosity and those determined from sedimentation or diffusion rates, for certain cellulose esters and starch derivatives. Effects of solvent and of inhomogeneity in respect to molecular weight are discussed briefly.
13(1945); http://dx.doi.org/10.1063/1.1724021View Description Hide Description
The mechanical laws of impact lead to the conclusion that, in any transfer of kinetic energy into quantized energy (excitation, dissociation), the ``excitation function'' should, at the threshold, start from zero and increase with increasing kinetic energy. This shape of the function is likely to cause a systematic error in the measurement of critical energies with certain non‐equilibrium methods.