摘要:

AbstractA method of determining the osmotic pressure of a solute which can diffuse through the membrane is described. It is shown theoretically that after a certain time interval a plot of the logarithm of the indicated osmotic pressure against time yields a straight line which can be extrapolated to zero time. The true value of the initial osmotic pressure is calculated by correcting the extrapolated value for the rate of transfer of solute and solvent through the membrane and for the partition coefficient of the solute between the membrane and the solvent. The various correction factors are calculated from experimentally determined quantities. By the use of cellophane membranes, osmotic pressures of lignin sulfonates with molecular weights as low as 4,300 have been evaluated.

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611401

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractAn x‐ray diffraction study has been made of cellulose triacetate II. Small films of highly crystalline triacetate with good fibrous orientation and a fair degree of biaxial orientation have been prepared by repeated rolling at successively higher temperatures between 160 and 215°C. The x‐ray diffraction patterns exhibited several new reflections which made it possible to determine the unit cell. It has been found that cellulose triacetate II has four cellobiose acetate residues in a pseudo‐orthorhombic cell witha= 24.5,b= 11.56, andc= 10.43 A. Pairs of these residues are related by twofold screw axes in thecor fiber‐axis direction. The paired arrangement seems to be determined by a fitting of the natural zigzagging shape of the cellulose backbone which is exaggerated by the presence of the secondary acetyl groups. The glucose residues of such a pair are parallel and inclined at about 45° with respect to theaaxis. A neighboring chain pair points in the opposite direction and the median planes of the cellobiose units of two such pairs are approximately mutually perpendicular. To accommodate this type of packing, one half of the primary acetyl groups must be twisted sharply out of the median plane of the parent glucose residues. A second statistical model which basically is very similar is also considered. There do not appear to be any strong interactions betwe

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611402

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractCotton and wood cellulose were irradiated with gamma rays within the dosage range 60 X 103r to 2,300 X 103r. A measure of the degradation was obtained from intrinsic viscosities obtained from viscosity determinations in cupriethylenediamine solution. The presence of water had no significant effect on the extent of radiation‐induced degradation. Thus there was little or no difference between the results on irradiated samples of wood cellulose containing 3.3, 4.6, and 5.6% moisture. Cotton cellulose irradiated in the presence of excess water or 3.5% moisture was equally degraded. At lower moisture levels (0.26–0.32%) an aftereffect was observed in which the solution viscosities of the irradiated samples progressively decreased up to 30 days in storage. The duration of the effect was independent of the dosage levels studied. From the experimental results reported here and from recalculations of data in the literature the radiation threshold dosage for isolated celluloses appears to be in the range of 28.4 to 81.2 X 103r. Cellulose is degraded at gamma‐radiation dosages equal to or below those required for softening plant tissues such as apples, carrots, and beets. Therefore it seems probable that the degradation of this cell wall constituent is a major factor in the radiation‐induced softening of plant

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611403

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe polymerization of α‐methylstyrene catalyzed by sodium naphthalene has been studied below 0°. Measurable amounts of monomer remained in equilibrium with the polymer down to −40°, even though the color indicated that active chain ends were still present. This behavior is expected of α‐methylstyrene since, due to a low heat of polymerization, the reverse of the chain propagation step must be important at these temperatures. From the equilibrium monomer concentrations determined experimentally, the heat and entropy of polymerization of α‐methylstyrene has bee

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611404

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe well‐known Zimm plot can be modified by plottingKc/Rϑsin2(ϑ/2) against 1/sin2(ϑ/2) with concentrationcas a parameter, which gives a series of straight lines with a common intercept. By extrapolating to zero concentration one can determine the weight‐average molecular weight from the reciprocal of the slope and the radius of gyration from the common intercept on the ordinate. This method finds applications for macromolecules having very high molecular w

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611405

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe stabilization energy due to the conjugation taking place between a monomer and an ion in the transition state is calculated by the LCAO perturbation theory, in the same way in which the reactivity in radical copolymerization has previously been treated. In terms of this stabilization energy, the reactivity ratios of several monomer pairs in ionic copolymerization are satisfactorily interpreted. It is noted that, by the present method, both the radical and ionic copolymerization can be treated in a unified manner, whereas it is difficult in existing empirical methods. The positions of attack in polymer ions as well as in monomers, which are predicted by the frontier electron densities, are shown to agree well with experimental facts. The relative reactivities of vinyl monomers in ionic homopolymerization is also explained successfully by the magnitude of the localization energy computed by the LCAO method.

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611406

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractMeasurements were made of the infrared absorptions of ethylene glycol and polyethylene glycols (from a dimer to a heptamer) in liquid state. In the case of polyethylene glycols, three distinct peaks appear in the wave number range of CH2rocking modes. This affords a conclusive evidence in support of the existence of thetransform as well as thegaucheform of the O(CH2)2O portion of linear chains. This confirms the result of dipole moment measurements that bothgaucheandtransforms are realized in the configurations of the lower members of polyethylene glycols in solution. Although it is reported that high molecular polyethylene glycol in crystalline state assumes a highly crumpled helical structure resulting from thegaucheminima, the molecular structure of low molecular polyethylene glycols is not restricted to the same helical configuration. These chain molecules take a more or less irregular form resulting from thetransandgaucheminima of the internal rotation about single bonds. Ethylene glycol shows only two absorption peaks in the wave number range of CH2rocking modes. A plausible explanation is presented based on the formation of intramolecular hydrogen bo

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611407

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractA new technique which permits of the use of boron‐trifluoride for catalysis of epoxy polymerizations is described. The destructive exotherm that ordinarily accompanies contact of this substance with epoxy compounds is avoided by gradual release of the catalyst. This controlled release is accomplished through use of the catalyst in the form of the liquid boron trifluoride‐ethyl ether complex absorbed on a particulate carrier, the component particles being coated with a paraffin barrier layer. Employing this catalyst system a smooth but rapid reaction is obtained starting with all reactants initially at room temperature and without application of external heat. Polymerization is essentially complete within several minutes following addition of the catalyst sys

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611408

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractA general criterion for gelation in polycondensations having like groups of unequal reactivity has been formulated. In its simplest form, the criterion is that, for gelation, the expectation that a given structure will be propagated is unity, or greater. Several specific cases are treated, and literal expressions relating the gelation point to the reaction probabilities are derived. Included are treatments of systems involving anhydrides and mixtures of acids and glycols. The manner in which kinetic calculations may be used to determine reaction probabilities is summarized. It is found that the inclusion of unsymmetrical reactants significantly increases the degree of polymerization necessary for gelation. However, when anhydrides are used, depending on the relative reaction rates of the anhydride and the acid formed when the anhydride reacts, the degree of reaction necessary for gelation may be either greater or less than that for a similar system using only symmetrical reactants.

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611409

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractCeiling temperaturesTc(at which the free energy change for the reaction is zero) have been determined for the formation of polysulfones from a wide variety of olefins and allyl compounds under standard concentration conditions ([M] [S]= 27 mole2liter−2, M = unsaturated compound, S = sulfur dioxide). In the 1‐olefin seriesTcfalls from ethylene to propylene 90°, to 1‐butene 64°, and then remains approximate constant as the chain is lengthened. With 2‐olefins there is a progressive decrease from butene 34°, to pentene 8°, to heptene −38°. Branching invariably lowersTcand the effect is greatest when the branching is at the double bond; thus isobutene 4°, 3‐methyl‐1‐butene 36°, 4,4‐dimethyl‐1‐pentene 14°. 2‐ethyl substitution of a 1‐olefin, or 2, 3, or 4 branching of a 2‐olefin results in inability to react (Tc<−80°). Cycloolefins haveTcvalues considerably higher than the corresponding 2‐olefins; thus cyclopentene 102°, cyclohexene 24°. In the allyl compounds a carboxyl group tends to lowerTcbut a hydroxyl group raisesTc. An ether group raisesTcslightly. The results are discussed in terms of structural effects on the heat and entropy changes and on the monomer activity coefficients and polymer solubilities. The infrared absorption spectra of 20 polysulfones and 3 aliphatic sulfones are recorded for

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202611410

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY