摘要:

AbstractThe molecular weight, the size, and the second virial coefficient have been determined for a series of styrene polymers prepared under high pressure (0 to 4000 atmospheres) using light scattering techniques. The intrinsic viscosity–molecular weight relationship, the size–molecular weight relationship, and the magnitude of the second virial coefficient reveal no significant differences when compared to similar data of regular polystyrene. Structural differences due to the method of polymerization do not exist to the extent that they can be revealed by such measureme

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120112

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractRefractive indices of five polythene samples, previously studied by Bryant and Franta and by Muthana and Mark, who determined their densities, degrees of branching, osmotic molecular weights and μ‐values in xylene solutions, have been measured by the immersion method in suitable liquid mixtures. Powdered samples have been prepared from xylene solutions by cooling and by evaporation of the solvent under identical conditions. They appear, under the microscope, as transparent radial and weakly birefringent spherulites; refractive index values are higher than those of the amorphous polythene and decrease as the degree of branching increases. The refractive index lowering is to be ascribed to the change both of the molecular structure (branching) and of the ratio between the amount of amorphous and of crystalline material, the latter strictly depending on the former when samples are prepared under identical conditions. Measurement of the refractive index may therefore be suitable for the empirical determination of the degree of branching in polythenes; it seems to be simpler and more significant than the measurement of the density, the latter also being affected by relatively large microvoids, while the refractive index may be affected only by those microvoids the sizes of which are not larger than the wave length of the light used. Refractive index measurement may also be suitable for the determination of the degree of branching and of the degree of crystallinity in other polymeric substanc

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120113

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractThis paper reviews some aspects of the present state of research in the field of polyelectrolyte solutions. It deals mainly with synthetic polyelectrolytes with special attention to their electrostatic potentials, the colligative properties of their solutions and molecular shape changes.

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120114

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120115

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractThe finding of Pouyet and Sadron that, at extreme dilutions of thymonucleic acid, the specific viscosity at low shear rates is either unaffected or only slightly affected by salts is confirmed with two samples prepared in different ways. The specific viscosity in these solutions increases considerably above the limiting value at very low concentrations and is then markedly sensitive to the presence of salts even at very small concentrations of the latter. The rapid increase of the specific viscosity with increasing concentration must be due to increasing interaction between the particles, and as these interactions are sensitive to small salt concentrations they must be electrostatic in nature. It is suggested that they arise from the Debye‐Hückel forces between the particles and their counter ions. When no added salt is present the counter ions can only complete their ion atmospheres by interacting with two of the polyelectrolyte particles and this will give rise to interactions between the particles, which will be greatly reduced by even small concentrations of added electrolytes. Interactions of this type will vary in strength according to the distances of the interacting charges and may be so weak that the shearing stresses can over come them. This will produce the high shear dependence observed in solutions of this kind. The differences between the behaviour of deoxyribonucleic acid and various synthetic polyelectrolytes which have been studied may arise from the fact that in the former the charges are carried by the “backbone” of the fiber and in the latter on side chains which are capable of ro

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120116

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractThe sedimentation constants and diffusion coefficients of sodium polymethacrylate and of polymethacrylic acid have been determined at various concentrations of polymer and of added electrolyte and the nature of the charge effects is considered. A ratioy= (molarity of added electrolyte)/(grundmolarity of polymer) is used to obtainS20aty= ∞ when the polyelectrolyte is assumed to be uncharged. The variation of the effective radius withyis considered not to be due to asymmetry but to the open network nature of the polyelectrolyte coil.The sedimentation constant of unionized polymethacrylic acid is determined and also the variation of sedimentation constant with degree of ionizatio

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120117

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractThe interactions of some polyelectrolytes (anionic–gum arabic, agar; ampholytic–gelatin) with silver bromide solin statu nascendiwere studied. It was found that there are analogous phenomena to those encountered with usual hydrophobic sols. The polyelectrolyte effects on hydrophobic systems were treated in a manner usual for simple electrolytes. The appearance of the typical coagulation curves with maximum is used for the characterization of various systems: hydrophobic colloid–polyelectrolyte–electrolyte. Depending upon the position of the system on “stabilizing” or “sensitizing” side of this maximum (sometimes of minimum), there is a very pronounced difference of the polyelectrolyte action on the coagulation value of simple electrolyte. Thus, on the “stabilizing” side, the “reverse” antagonism was found, which is explained as a result of the dominating polyelectr

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120118

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractA carboxymethylcellulose sodium salt (CMC) with about 50% of the glucose units substituted, has been studied dielectrically by the “ellipsoid method” at various wave lengths. Aqueous solutions containing 0.1–0.0025 g./100 ml. were investigated. Dielectric increments of 2–9 dielectric constant units were obtained for these solutions. The calculated increment per gram per liter was not constant but increased considerably at the lowest concentrations, indicating the prevalence of polar molecules or aggregates at the lowest concentrations, whereas less polar aggregates dominate at higher concentrations (more than 0.01% solutions). At the lowest concentration studied, 0.0023%, the increment per gram per liter was about 120, corresponding to a molar increment of about 55,000,000. Dielectric dispersion curves were obtained which approached theoretical Debye dispersions, indicating that the CMC molecules are rather rigid. The dispersion curves were displaced toward shorter wave lengths with increasing concentration, probably due to the strong molecular interaction. At the lowest concentration a relaxation time of 4.6 × 10−7sec. was calculated for the CMC molecule. This corresponds to a rotation of the molecules about their long axes in the electric field. An average molecular weight of about 460,000 was calculated for the CMC molecules, or polar aggregates, in very dilute aqueous solution. The electric moment of CMC was estimated to be about 1000 Debye units. In contrast to CMC, the uncharged polysaccharides dextran and ethyloxyethylcellulose did not show any deviation of the dielectric constant values from that of the pure solvent, when investigated in 0.5% aqueous solutions at various wave lengths. It was concluded that the dielectric properties of CMC are very similar to those of other polyelectrolytes studied–such as desoxyribonucleic acid, nucleohistone, and hya

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120119

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractThe salts of carboxymethylcellulose (CMC) are used in large quantities to improve the dirt‐suspending power of synthetic detergents and soaps. Hardly any attention has been given to the question as to which properties they should have to obtain the greatest suspending power. They exert their specific influence because they are adsorbed by cellulose fibers from their solutions in water. Theoretical considerations are given, showing that: (1) The degree of substitution (DS) should probably be about 0.5. (2) The substitution should be as uniform as possible. (3) The cellulose chains should be neither too short nor too long. Normally only the average degree of substitution, DS, is determined. The fiber contents, FC,i.e., the percentage of insoluble and partly swollen fibers in 1/20NNaOH can be taken as a measure of the uniformity of the substitution. Technical products differ greatly inpH and salt contents; therefore the viscosity of solutions of the technical products containing 1% of the cellulose ether, to which 2.5% Na2CO3and 2.5% NaHCO3have been added, is taken as a measure of the length of the cellulose chains. The easiest way to obtain uniformly substituted products is by dispersing cellulose and reagents in a suspending liquid,e.g., an alcohol or a hydrocarbon. FC's smaller than 2 to 4% are obtained. Then the dirt‐suspending power was greatest with a DS between 0.48 and 0.53; and a viscosity measured as above with a Hoeppler standard viscometer between 11 and 29 c.p.s. The substitution in general is much less uniform when CMC is prepared according to the customary method by mixing cellulose, NaOH, and ClCH2COONa or ClCH2COOH and a little water. Then the results were best with an average DS between 0.51 and 0.60, and an FC between 6 and 16%, said viscosity being 20 to 30 c.

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120120

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY

摘要:

AbstractIt is now becoming possible to correlate studies on the general size and shape of protein molecules in solution with knowledge of the possible configurations of polypeptide chains and, in some instances, with that of the actual sequence of amino acid residues in these chains. The formation of helices and of “pleated sheets” from polypeptide chains, and the dimensions of these structures, are discussed, and the possible significance of proline residues for the bending and folding of chains is pointed out. The relation of purified protein preparations to the state of the proteins in their natural surroundings is discussed, as is the meaning of the concept of purity. Protein molecules are to be regarded as highly ordered and regular structures, but probably not as completely rigid. The meaning of the concept of protein hydration is considered, with reference to both external and internal hydration. The question of what can be learned from hydrodynamic measurements concerning the hydration and the shapes of protein molecules in solution is critically discussed.The evidence available today concerning the size and shape of some particularly wellknown proteins is examined. These include beef insulin; horse heart myoglobin; horse hemoglobin; human and bovine serum albumin, including mercaptalbumin; human and bovine fibrinogen; rabbit myosin; and tobacco mosaic virus. The first three of these molecules are relatively small and symmetrical in shape. Serum albumin appears to be moderately asymmetrical, with an axial ratio of the order of 4 to 1. Fibrinogen, myosin and tobacco mosaic virus are highly asymmetrical. Although the chemical structure of insulin is now known in great detail, the shape of the molecule as a whole cannot yet be precisely specified. All the molecular models proposed for these proteins, except perhaps that for the virus, must be regarded as tentative and subject to revision.Future prospects of progress in this area are considered, with particular emphasis on the significance of dielectric dispersion, fluorescence polarization, and x‐ray methods. The hope of obtaining fairly rapidly a much deeper insight into protein structure now appears justif

ISSN:0022-3832    

DOI:10.1002/pol.1954.120120121

出版商:Interscience Publishers, Inc.    

年代:1954

数据来源: WILEY