ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310301

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe vaper pressure of ethyl acetate‐natural rubber mixtures has been studied at 25 and 50°C. over the whole range of miscibility. Current statistical theories of polymer solutions fail to account quantitatively for the observed entropy of mixing; the discrepancy is attributed to the occurrence in this system of non‐random mi

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310302

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractOn a préparé une série de dérivés du n pentatriacontane, considérés comme substances modèles de macromolécules. Leurs solutions benzèniques diluées, ont permis d'étudier l'influence du substituant sur l'énergie libre molaire partielle\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\Delta F_0 } $\end{document}du solvant, en particulier sur le deuxième coefficientA2du développement de\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\Delta F_0 } $\end{document}en série de puissances de γ, la concentration molaire du soluté. Les coefficients ont été comparés directement à celui de la substance mère par la méthode de la distillation isotherme. II apparait que le branchement augmenteA2, alors que l'ablation d'un CH2de la chaǐne ou un substituant phényl n'ont que peu d'influence. Le substituant Cl, et plus encore I'introduction d'une double liaison font au contraire décroǐtreA2. Dans ce dernier cas, on a pu constater que l'effet est additif (si les deux doubles liaisons sont assez éloignées) et indépendant de la position de la double liaison dans la chaǐne. La mesure directe de la chaleur de dilution semble donner la somme de la vraie chaleur de dilution, plus une chaleur de désorbtion. Ces chaleurs mesurées sont relativement peu différentes d'un produit à l'autre. Leurs différences permettent d'estimer l'influence de ces substituants sur l'entropie molaire partielle du solvant\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\Delta S_0 } $\end{document}en particulier sur le deuxième coefficientbde son développement en série de γ. On retrouve sen

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310303

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractOsmotic pressure, initial phase separation, and viscosity results are presented for dilute solutions of cellulose nitrate, cellulose acetate, and ethyl cellulose, using polymers of similar molecular weight and degree of substitution. A fairly wide range of solvents has been used in each case. Osmotic pressure results suggest molecular dispersion of polymer in most solvents but there is evidence for association of ethyl cellulose in aromatic hydrocarbons. Values of the Huggins μ are obtained and, for systems involving cellulose nitrate and ethyl cellulose in homologous series of ketones and acetates, seem to fall to a minimum and then increase on ascent of each series. It is suggested that the heat term in μ should include an exothermic contribution arising from solvation in addition to an endothermic contribution resulting from mixing of solvated polymer and solvent. It is tentatively suggested that, in a homologous series of solvents, the entropy and exothermic contributions may not vary much and that the variation of μ may arise from varying endothermic contributions. The volumes of hexane required to cause initial phase separation of the nitrate and acetate from solution increase with solvent power, as estimated from μ, but with ethyl cellulose the volumes tend to decrease. It is suggested that solvated polymer may separate from solutions involving polar solvents and, making certain assumptions, estimates are made of the solubility parameters of the polymers separating. Those for cellulose nitrate vary markedly with solvent. The variation of solubility parameter with solvent is less with cellulose acetate and ethyl cellulose but in the latter case values for polymer separating from polar solvents are less than from nonpolar. Comparison of these estimated solubility parameters with those of the solvents and hexane suggests that the volumes of hexane required to cause initial phase separation will only serve as measures of solvent power if the solubility parameters of solvents and precipitant all lie on the same side of that of the polymer separating. This seems to be so for cellulose acetate and possibly the nitrate but not for ethyl cellulose. Comparison of viscosity parameters and values of μ suggests that in certain cases both [η] and the initial slope of the plot of ηsp/cagainstcincrease with solvent power. Other suggested viscosity measures of solvent power do not seem to be generally applicable. Some variation of chain configuration with solvent seems probable. Solvation, solvent type and association of polymer may also affect the viscosities of dilute solutions of cellulose deriv

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310304

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe swelling and solution of elastic polymers, like the mixing of liquids, results in the formation of equilibrium systems. In the interaction of conventional glasses and liquids, however, quite different phenomena appear and cause nonequilibrium systems to form. The density of molecules in conventional glasses is similar t o that of tightly packed liquids, but the diffusion rates are very low. Such glasses sorb practically nothing at low vapor pressures. Sorption begins only when the vapor pressure and the concentration of sorbed liquid in the surface layer are sufficient to cause the glass to melt. It should be noted that in this case sorption shows a sharp rise and an equilibrium solution forms. The degree of tight packing of polymeric glasses varies considerably, decreasing with increasing molecular weight and rigidity of the chain molecules. This packing can be estimated by comparing the densities of the polymers with the volume of the molecular groups of which these polymers consist, the latter being obtained from x‐ray data, or by comparing the density of the monomer with that of the polymer. Cellulose, which unlike tightly packed glucose sorbs water over the whole range of vapor pressures, is a typical example of a loosely packed polymer. The effect of the density of packing on the sorbing properties of glasses can be more clearly demonstrated by the sorption of ethylbenzene by polystyrenes of different molecular weights. Low molecular weight polystyrenes dissolve in ethylbenzene without any heat production and sorb ethylbenzene from the vapor at high pressures only. This process results in the formation of a solution. High molecular weight polystyrenes, however, dissolve in ethylbenzene, producing heat, and sorb ethylbenzene a t all vapor pressures. The loose packing of polymers is the result of the long relaxation times existent in glasses. When the deformation time of the polymer is less than the volume relaxation time, the polymer becomes porous. Thus both the sorbing properties and the heats of solution of polystyrene become more pronounced during orientation. The degree of tight packing again increases at heats close to the glass point. Thus polymeric glasses hold an intermediate position between liquids and hard porous sorbents, such as silica gel, in regard to their sorbing properties. Unlike hard sorbents, however, they are apt to change their structure not only under external influence but also in the process of sorptio

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310305

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractSimultaneous measurements of osmotic pressure and permeation of solute have been made for a nonfractionated polystyrene with a number of membranes of widely different permeability. It is shown that, even after many days, no real equilibrium is reached in an osmometer with a membrane permeable to part of the polymer. The theory of equilibria in such osmometers is developed and shows that, in first approximation, the distribution of permeating solute over the two osmometer cells is not affected by the presence of nonpermeating solute. In second approximation, this distribution is affected indeed, but in this approximation the osmotic pressure is not affected by this unequal distribution. Some short‐time experiments also show that when the number of permeated molecules is negligible (t→ 0) the contribution of a molecular species to the osmotic pressure is less than the value given by equilibrium thermodynamics if the membrane is not completely impermeable to that molecular species. This phenomenon is in accordance with the theory of permeability of membranes based upon nonequilibrium thermodynam

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310306

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractAn osmometer has been constructed in which the only possible transition from one cell to the other is through the vapor phase. In this way the problem of passage of solute is completely eliminated. In order to obtain a sufficient rate of transition of solvent, the distance between the cells has been made as small as possible. An osmometer with a vapor “membrane” of 0.05 mm. thickness is described and measurements with this osmometer are repor

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310307

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractSix polystyrene fractions of molecular weights ranging from 1,300 to 250,000 were dissolved in amyl acetate a t various temperatures. The velocity of dissolution was measured by the increase in the refractive index. An assumption was made to describe the experimental results, namely, that the adhesive layer on the surface of solid polystyrene in solvent consists of macromolecular coils the diameter of which can be calculated by Flory's formula. Comparison of the value of the exponentA(fromMA) obtained from viscosity measurements with the value calculated from the velocity of dissolution shows excellent agreement. The temperature dependence of the velocity of dissolution is dependent also on the diffusion process of the solvent molecules into the polymer. The expression for this diffusion derived by considering it, as usual, as a rate process, can be introduced into the equation for the velocity of dissolution. The resulting equation accurately describes the experimental results. The velocity of dissolution is different above and below the glass temperature of the polymer. It is possible to use the velocity of dissolution for a determination of molecular weight if the constant of the apparatus has been found by means of a standard sample of known molecular weight. This method helps in the difficult range of molecular weights from 5,000–40,000, where it is very sensitive, whereas other methods are no

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310308

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractDans le but d'étudier le comportement physicochimique de diverses molécules à chaǐne courte, monodisperses et sans ramifications, nous avons fait une série de mesures viscosimétriques comparatives sur des paraffines normales d'une part, et d'autre part sur des dérivés oxygénés: éthers, dialcoxyalcanes, dialcoxydiéthyléther, etc… Toutes ces mesures ont été effectuées en solution diluée, dans le tétrachlorure de carbone et dans le benzène. Les résultats font apparaǐtre que: (1) Dans le cas des paraffines la viscosité intrinsèque devient négative si la chaǐne comporte moins de dix chaǐnons. Les résultats expérimentaux sont valablement représentés par une loi de la forme [η] = −A+BlnN. (2) Le remplacement d'un CH2par un atome d'oxygène entraǐne une augmentation de [η]. L'ensemble de nos résultats—paraffines et dérivés oxygénés—peut ětre représenté par une loi de la forme\documentclass{article}\pagestyle{empty}\begin{document}$$ [\eta ] = ‐ A(X_0 ) + B(X_0 )\ln {\rm }N $$\end{document}AetBétant des fonctions du rapport du nombre d'atomes d'oxygène au nombre total de chaǐnons de la chaǐne. (3) Le comportement des deux solvants étudiés à l'

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310309

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractSolutions of polyisobutylene in tetralin were observed to show antithixotropy. Quantitative results are given, and comparison is made with a non‐Newtonian liquid of constant viscosity and with one which shows (positive) thixotrop

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202310310

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY