摘要:

AbstractLight scattering measurements were made on amylopectin prepared from potato starch by two procedures. Potato starch dispersed in water at 90° and fractionated with mixed pentanols gave an amylopectin I having a weight‐average molecular weight of 36 million. Dispersion of starch by autoclaving at 120°, followed by nitrobenzene precipitation of amylose, yielded an amylopectin II with weight‐average molecular weight of 14 million. No evidence was found for dissociation of these amylopectins into smaller units in aqueous solution at concentrations as low as 10−6g./ml., at elevated temperatures, or in sodium hydroxide solutions. Aggregation of amylopectin II occurred at potassium chloride concentrations above 5 × 10−4molar. Marked reduction of molecular weight of amylopectin II resulted from treatment under a high rate of shear in a Waring Blendor. Acetylated II (40% acetyl content) was soluble in nitromethane, chloroform, acetone, dioxane, and acetonitrile. In all these solvents the molecular weight, corrected for acetyl, was close to 10 million. No evidence was found for an increase in reciprocal specific turbidity at low concentration which would parallel reported osmotic pressure results. Polydispersity was demonstrated by ultracentrifugal sedimentation patterns of amylopectin II, and by separation of amylopectin I into a series of fractions ranging from 7 to 73 million in molecu

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168101

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractUltracentrifugal studies on polystyrene latex particles (PSL) in solutions of different densities prepared either from mixtures of H2O and D2O or from various concentrations of sucrose in water yielded a value, by interpolation, of 1.0520 for the density of solution in which the particles neither sediment nor float. Considerations of these results plus the nature of the particles lead to the conclusion that the partial specific volume of the polystyrene latex particles is (1/1.0520) cc./g., a value in agreement with the bulk specific volume of solid polystyrene. Evidence is presented for PSL to support the view that the effective hydrodynamic volume is equal to the partial specific volume, so that volume fractions can be determined from the partial specific volume and the dry weight concentration. Measurements of the viscosity of suspensions of polystyrene latex particles over a broad concentration range showed that the intrinsic viscosity was 2.5, in confirmation of the theory of Einstein. At concentrations above 2% by volume a square term in concentration, with coefficient about 10, and also a cubic term are needed to satisfy the data. From the partial specific volume of the latex particles and the value of the sedimentation coefficient extrapolated to infinite dilution, a value of 2640 ± 12 A. was calculated for the diameter of the particles from Stokes' law. This value is in excellent agreement with values obtained by electron microscopy, light scattering, and low angle x‐ray scattering. This agreement amounts to a satisfactory test of Stokes' law for particles not much larger than some of the viruses. Studies of the dependence of sedimentation coefficient on concentration indicate that existing theories are not completely satisfactory and that the influence of backward flow of liquid during the sedimentation of the solute particles is appreciab

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168102

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe polymerization of vinyl acetate has been studied at temperatures down to −40°C. by means of a specially designed apparatus. The object of the experiments is to preparer polyvinyl acetates of as linear a character as possible by working at low temperatures in order to avoid transfer reaction to accumulating polymer. Polymers prepared at a number of temperatures have been examined osmotically and by the light‐scattering technique. Using the latter technique, it has been shown quite clearly that the size of the molecule, as measured by the dissymmetry measurements, gets smaller and smaller for a given molecular weight as the temperature of synthesis is decreased. It is believed that if the synthesis is carried out at temperatures below −30°C., then the molecules formed are predominantly linear in ch

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168103

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractAbsorptionsmessungen an Lösungen von reinstem γ‐Globulin, das einmal in nicht assoziiertem, ein zweites Mal in assoziiertem Zustand vorlag, liefern folgende Ergebnisse: (1) Die Tyndall‐Absorption gehorcht der Rayleigh‐Beziehung ε ′T=K·v′nwobei sowohl ausserhalb, als auch innerhalb des Gebietes der Konsumptivabsorption die GrössenKundninnerhalb der normalen Fehlerbreite konstant bleiben. (2) Im Gebiet der Konsumptivabsorption darf Additivität zwischen konservativer und konsumptiver Lichtabsorption angenommen werden. Die mitgeteilten Ergebisse werden als Stütze für die Zulässigkeit der bisher angewendeten Korrek

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168104

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractPolyethylene succinate, prepared by condensation in solvents, has been fractionated into 6 fractions by repeated solvation and precipitation. Molecular weights of the fractions have been obtained by cryoscopic and titrimetric measurements. Dilatometric measurements at various temperatures gave the specific volumes of all fractions. The melting point (Tm)‐molecular weight relationship follows the function:\documentclass{article}\pagestyle{empty}\begin{document}$ {1 \mathord{\left/ {\vphantom {1 {T_m }}} \right. \kern-\nulldelimiterspace} {T_m }} = 2.59 \times 10^{ - 3} + \left( {{{0.79} \mathord{\left/ {\vphantom {{0.79} M}} \right. \kern-\nulldelimiterspace} M}} \right) $\end{document}The velocity of crystallization of the polyester has been calculated from the change of volume with time during crystallization. It has a maximum at 30°C. for all chain lengths. The reciprocal half‐time of crystallization at the same temperature of crystallization decreases with increasing molecular weight of the polyester and finally approaches a limiting v

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168105

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractFrom electron micrographs of clonal latices and centrifuge fractions, the particle size distributions inHevea brasiliensislatices have been measured. By means of this investigation–which was meant to be informative only–it has been possible to ascertain that the highly asymmetric size frequency distributions that are apparently present result from the existence of several size fractions, which each itself has a normal Gaussian distribution. The particle sizes are found as being multiples of whole numbers of either of the two particle sizes 58 mμ and 69 mμ. A possible explanation of this phenomenon is that the larger particles form by clustering of the smaller particles in a grape‐like arrangement, without actual coalescence or fusing together. From the experiments it may be supposed that the particle size distribution of latex may have an influence on its centrifuging qu

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168106

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168107

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168108

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1955.120168109

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY