摘要:

AbstractRecent literature reports from three laboratories have treated the refraction correction for the Sofica and a noncommercial light scattering photometer. Our re‐evaluation of the data contained in these reports, as well as our experiments, indicate that the usually citedn2refraction correction has not been unquestionably established for these instruments. In some cases, imprecise experimental techniques have been used to support this particular form of the correction. In addition, we find the optical system of the Sofica instrument results in the detector seeing vertically past the horizontal edge of the illuminated volume in violation of a basic assumption in the deduction of then2correction. Our experiments, as well as our interpretation of recent literature data, support an exponent of less than 2.0 for the Sofica apparatus, which is consistent with an instrument whose detector views outside the illuminated volume. However, the experimental methods available to evaluate the exponent lack the desired precisio

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100201

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe present work is a continuation of a general study of the effect of pressure on gas and vapor permeation through nonporous polymeric membranes. Permeability coefficients have been measured for 1,1‐difluoroethylene (C2H2F2) and fluoroform (CHF3) in polyethylene at penetrant pressures up to 35 atm and at temperatures between ‐18 and 70°C. The permeability coefficientP̄for the 1,1‐difluoroethylene—polyethylene system was found to increase with increasing pressure differential Δpacross the membrane. Isothermal plots of log ΔPversus Δpare generally linear and can be represented by empirical relations of the form ΔP=P(0)exp{mΔp}, whereP(0) andmare constants. The slopemof these isotherms decreases with increasing temperature. Plots of logP̄versus Δpfor the fluoroform—polyethylene system are also linear, but exhibit negative slopes, i.e.,P̄decreases with increasing Δp. An extension of Fujita's “free volume” theory of diffusion in polymers shows that the dependence ofP̄on pressure reflects how the free volume of the polymer is affected by this pressure. An increase in the penetrant pressure may result in two opposing effects: (a) the concentration of the penetrant dissolved in the membrane is increased, thereby increasing the free volume, and (b) the hydrostatic pressure on the membrane is also increased, which causes a decrease in the free volume. If the overall effect is an increase in the free volume of the polymer, thenP̄will als

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100202

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractShort aliphatic polymer chains of different lengths were prepared by degrading polyethylene samples of appropriately chosen initial fold lengths to the chain lengths which correspond to a single chain traverse through the lamella. The resulting dicarboxylic acids were either used as such for further crystallization experiments or were first converted into diiodides to remove polar endgroups. The resulting short polymers all crystallized by chain folding even if the chains (peak of distribution) were only 1.5–4 times the length of a traverse through the lamella. In the diiodides the fold length varied continuously with crystallization temperature, as is usual in high molecular weight material, but with the dicarboxylic acids such variation, while observable, was only small. The effect of the molecular weight on the fold length due to its influence on supercooling at a given crystallization temperature has become apparent. Renewed degradation with nitric acid and subsequent GPC analysis of the degradation products confirmed the folded nature of the chains in the above crystals. This analysis combined with experiments on the reactivity of chain ends has led to the picture that each chain folds completely, once, twice etc. so that both folds and ends are in the surface zone but are located at varying heights, as appropriate to the overall layer thickness for the molecular weight distribution in question. This picture is consistent with other concurrent wor

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100203

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractAs a continuation of the preceding study on the folding behavior of short polymer chains, an iodine‐terminated paraffin having 156 Å peak molecular length and a sharp molecular weight distribution was prepared. The paraffin could be crystallized in lamellae of two different thicknesses: (A) thickness close to half the chain length (the most readily obtained); (B) thickness intermediate between half chain length and fully extended chain. Case A corresponds to each chain folding once with equal stems and with ends at the surface. Degradation behavior revealed that the folds must be of closely equal length giving rise to an even fold surface. In case B the situation is more involved: here the chain ends must turn into the lattice. Adjacent reentry is a necessity throughout. In both cases the lamellar thickness could be increased by annealing up to complete chain extensi

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100204

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe effect of iodine sorption on the small‐angle x‐ray diffraction intensity is discussed in terms of the distribution of iodine sorbed in the amorphous regions of polymers. The change in the intensity of the peak corresponding to long periods is measured as a function of the iodine uptake in drawn, and annealed poly(ethylene terephthalate) films. A linear relation with slopeKis observed between the square root of relative intensity and iodine uptake. The slopeKvaries with annealing conditions. Theoretical values calculated for models of the distribution of iodine in amorphous regions, are compared with the observedK. Results can be interpreted on the basis of a “concave” distribution of iodine, i.e., with sorption sites more numerous near a crystal surface than in the interior of an amorphous

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100205

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractFlow birefringence experiments on aqueous solutions of poly(vinyl alcohol) and of methyl cellulose show that the optical anisotropy changes markedly during aging of the solution. The same effect can be obtained by adding alcohol to fresh aqueous methyl cellulose solutions. The flow birefringence was measured as a function of the velocity gradient on solutions with and without alcohol during the course of aging. The phenomena are attributed to intermolecular and intramolecular interactions between exposed hydroxyl groups of the polymer chains, as these are affected by a change in the degree of hydration during aging or by the addition of a strong hydrophilic agent such as an alcohol. Association or crystallization of the ordered polymer chains may occur and lead to a supermolecular structure in the solutions. By following Sadron's theory and making use of a polar diagram, it was concluded that, after aging or mixing with the additive, the solutions become optically heterogeneous and contain two different components with optical polarizabilities of the same [in poly (vinyl alcohol) solutions] or opposite (in methyl cellulose solutions) sign.

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100206

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractTen unfractionated poly(2,6‐diphenyl‐1,4‐phenylene oxide) samples were examined by gel permeation chromatography (GPC) and intrinsic viscosity [η] at 50°C in benzene, by intrinsic viscosity at 25°C in chloroform, and by light scattering at 30°C in chloroform. The GPC column was calibrated with ten narrow‐distribution polystyrenes and styrene monomer to yield a “universal” relation of log ([η]M) versus elution volume. GPC‐average molecular weights, defined asM̄gpc=\documentclass{article}\pagestyle{empty}\begin{document}$\Sigma w_i [\eta ]_i M_i /\Sigma w_i [\eta ]_i$\end{document},widenoting the weight fraction of polymer of molecular weightMi, were computed from the GPC and [η] data on the polyethers. TheM̄GPC were then compared with the weight‐averageM̄wfrom light scattering. The intrinsic viscosity (dl/g) versus molecular weight relations for the unfractionated poly(2,6‐diphenyl‐1,4‐phenylene oxides) determined over the molecular weight range 14,000 ≤M̄w≤ 1,145,000 are log [η] = −3.494 + 0.609 logM̄w(chloroform, 25°C) and log [η] = −3.705 + 0.638 logM̄w(benzene, 50°C). TheM̄w(GPC)/M̄n(GPC) ratios for the polymers in the molecular weight range 14,000 ≤M̄w≤ 123,000 approximate 1.5 according to computer integrations of the GPC curves with the use of the “universal” calibration and the measured log [η] versus logM̄wrelation. The higher molecular weight polymers (326,

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100207

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe elastic behavior of composite and interpenetrating network structures composed of non‐Gaussian chains is investigated. The chain probability density given by Nagai is employed utilizing only the leading correction terms for finite chain extensibility. The independent‐network hypothesis, proven valid in Gaussian statistics, is shown to be erroneous in non‐Gaussian systems. Further, it is found that composite networks composed of monodisperse chains are elastically isotropic, whereas a most probable contourlength distribution yields a large anisotropy but in the direction opposite to that observed experimentally for rubber. On the other hand, retention of the independent‐network hypothesis coupled with a most probable distribution successfully accounts for much of the observed anisotropy. Interpenetrating networks are shown to be substantially anisotropic when a most probable contour‐length distribution is

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100208

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractPermeability and diffusion coefficients for dimethyl sulfoxide (DMSO) in polyethylene have been measured by the “time‐lag” technique and found to be affected by the adsorption of DMSO vapor in the low‐pressure side of the apparatus. An analytical method is described for correcting the apparent permeability coefficients for such adsorption effects. “True” permeability coefficients for DMSO in polyethylene, expressed in units of cm3(STP) – cm/(sec‐cm2‐cmHg), vary from 0.92 X 10‐7at 30°C to 1.7 X 10‐7at 45°C, and their dependence on relative DMSO pressure appears to be small. The energy of activation for the permeation process is 7.1 kcal/mole. The described correction method is also applicable to the permeation of water vapor through polyethylene and poly‐(phenylene oxide). The apparent diffusion coefficients could not be corrected by this method. The solubility of DMSO in polyethylene was measured with a Bakr‐McBain balance and found to be very small; solubility coefficients are less than 0.8 cm3(STP) DMSO/(cm3polymer‐cmHg). It is concluded that the transport and solution behavior of DMSO in polyethylene is more similar to that of water vapor than to the correspondi

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100209

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe crystallization and melting temperatures of an unfractionated poly(2,6‐dimethyl 1,4‐phenylene oxide) (PPO) sample, PM2, were determined at 0.25°C/min cooling and heating rates in five binary toluene—PM2 and fifteen ternary toluene—polystyrene—PM2 solutions. The total polymer weight fraction range studied was 0.12–0.40 and the PM2 weight fraction range was 0.026–0.40. The heat of fusionHfof the PM2 was computed to be 10.1 cal/g from the melting point depressions. A toluene—PM2 pair interaction parameter χ13 = 0.890 – 223.5/Twas found. Although a reliable polystyrene–PM2 interaction parameter could not be computed, the data are consistent with χ23 = 0. Setting χ23 = 0 we calculate the toluene—polystyrene interaction parameter to be χ12 = 0.495 – 15.46/T. This χ12 is in remarkable agreement with values reporte

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100210

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY