摘要:

AbstractX‐ray diffraction patterns of stretched crystallized polybutadiene polymerized at −20°C were obtained using molybdenum, copper, and chromium characteristic x‐radiations on the same sample. The pattern obtained using molybdenum radiation showed diffraction effects in the 0, 1st, 2nd, 3rd, and 4th orders. The lack of detail in this pattern is partly due to the relatively intense background. By using the longer wavelength copper and chromium radiations the diffraction effects of the zero‐ and first‐order layer lines were brought out in considerable detail. The diffraction data obtainable from these layer line patterns may be useful in carrying out a structural analysis of crystalline pol

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030601

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractExperiments with cross linking of nitrocellulose in butyl acetate solution by means of titanium tetrachloride are described. The gels have been examined by means of sedimentation in the ultracentrifuge and measurements with a consistometer. The yield value of the flow curves and the extent of cross linking were studied as functions of nitrocellulose concentration, amount of cross‐linking substance, and time of reactio

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030602

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractThe fundamental basis of our work is the application of statistics involving both the energy of interaction between solute and solvent molecules and the effect of steric hindrances: the statistics of freely rotating chains (sometimes called the statistics of Kuhn) are a special limiting case. Using this we can show that in the law [η] =KNαthe coefficient is a function ofNhaving a value close to 2 for small values ofN, and approaching on first approximation a value of 0.5 whenNincreases infinitely. This statistical method has the advantage of permitting an approach to the important problem of the variation of the intrinsic viscosity as a function of the temperatureT.The behavior of intrinsic viscosity with degree of polymerization and temperature as predicted by the theory check with experiment, and, in the case of the hemipolystyrenes, it has been possible to obtain very satisfactory quantitative verification. In view of numerous experiments which show that, at a given temperature, the limiting value of α for very largeNis greater than 0.5, we have altered the theory of the equivalent particle accordingly. As a basis for the change the concept of porosity is examined with several other concepts, and it is shown that it is likely to apply only with reservations when the molecular structure of the solvent is taken into accou

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030603

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractIl est montré que le rapport entre la vitesse de propagation des ultra‐sons et la densité (u/p) des polymères est fonction de la forme des molécules. En particulier on trouve: (1) dans les composés à chaîne rigide paraffinique non ramifiée, ce rapport à la température de 20° s'accroît sensiblement avec le poids moléculaire de 1.67 pour les hydrocarbures du poids moléculaire bas à 1.92 pour le polythène à poids moléculaire élevé; (2) dans les composés ramifiés ayant des groupes méthyliques ou éthyliques, ce rapport est pratiquement constant pour tous les composés examinés jusqu'au poids moléculaire 15.000; (3) dans les composés linéaires contenants des groupes latéraux de dimensions plus grandes (p.e., phényliques ou oxybutyliques), ce rapport est plus petit pour les hauts polymères que pour les composés à poids moléculaire bas; (4) en général la compressibilité est plus élevé pour les polymères avec des ramifications fréquentes et longues que pou

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030604

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractEn cherchant à interpréter la courbe expérimentale de la titration potentiométrique de la viscose par l'AgNO3, 0.1N, on a découvert que les composés sulfurés de la viscose devaient se trouver sous la forme “ortho.” Ceci a permis de proposer une nouvelle théorie du mürissement d

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030605

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractThe decrease of the limiting viscosities of unfractionated and fractionated polystyrene with time has been studied over a range of temperatures from 248 to 340°C.in vacuo.Distribution curves of several degraded samples have been determined. It has been established that the theory of random breaking of links is not applicable in the case of polystyrene. Three major deviations from the random theory have been found. The experimental results have been evaluated employing the weak link theory. The mechanisms proposed account satisfactorily for the deviations from the random theory, and give a fair representation of the experimental results, only the experimental distribution curves still showing deviations from those predicted by theory. The elementary steps for the degradationin vacuohave been discussed and the role of oxygen during polymerization has been indicated

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030606

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractBy using the methods which have been developed to describe the activation energy of chemical reactions in terms of bond energies and the repulsing energies between reacting centers, the factors influencing the activation energies of reactions between radicals and monomers are discussed. Calculations are reported on a number of simple prototype reactions involving radicals and atoms and ethylenic bonds. It is found that the heat of reactions is a most important factor in determining the activation energies of such reactions and this result is extended to a wide variety of substituted radicals and monomers. The variation in the heat of reaction is expressed in terms of the resonance energies of the reacting radicals and molecules. Another important factor is the energy of repulsion between the reacting centers, and this energy is affected by (a) the charge distribution on the reacting centers and (b) the steric effect of substituent groups. The effect of substituents on the charge distribution is discussed in terms of the molecular orbital method, an attempt being made to distinguish between the influence on the π electrons of the inductive and mesomeric effect of substituents

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030607

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractPolyvinyl alcohol prepared by hydrolyzing polymerized vinyl acetate is partially degraded within a few minutes by reagents known to attack 1,2‐glycol structures. The degree of degradation is limited, however, the final molecular weights of the degraded products being in the range of 3700 to 6500 (viscosity averages). The extent of degradation seems to depend solely on the temperature at which the vinyl acetate was polymerized. Mole percentages (based on the structural unit CH2CHOH) of 1,2‐glycol structures, corresponding to head‐to‐head unit arrangements, have been computed from the degree of degradation with periodic acid. They increase from about 1.23% for polymerization at 25°C. to 1.95% at 110°C. The occurrence of head‐to‐head structures is attributed to occasional “abnormal” addition of monomer in the chain‐growth phase of the polymerization. The activation energy for the abnormal addition reaction is 1250 calories higher than for the normal (preferred) addition; the steric factor for the abnormal addition is about one‐tenth t

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030608

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

摘要:

AbstractAdditional data relating to the mechanism of the emulsion copolymerization of styrene and copolymerization of styrene and acrylonitrile are presented. These results show the influence of varying the emulsifier and of varying the water–monomer ratio upon the relationship between monomer composition and the composition of the initial copolymer molecules formed. The composition of the initial copolymer produced in emulsion is the same as that which would be predicted if polymerization occurred in the oil drople

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030609

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1948.120030610

出版商:Interscience Publishers, Inc.    

年代:1948

数据来源: WILEY