Wiley

A model is discussed which explains reported complex effects of feed composition and pressure on component permeabilities in high‐pressure gas separators based on glassy polymer membranes. A special form of Fick's law which accounts for the fact that penetrants in glassy polymers sorb into and diffuse through two different molecular environments provides the basis for the analysis of gas mixture permeation. Potential deviations from the theory are discussed in terms of separable solubility‐and mobility‐related effects.

Light scattering experiments are described on the system polystyrene (PS) + polyisobutylene (PIB) + toluene at constant temperature. At a fixed concentration of the nearly “invisible” PIB the light scattering at various angles was measured as a function of varying PS concentration up to the region of incompatibility. For interpretation of the results use is made of an extension of the classical fluctuation theory for multicomponent systems to finite scattering angles. The experimental data can be described qualitatively with this theory. Addition of a second polymer has little influence on the size of the other polymer. The variation of the light scattering with the wavelength can be explained in terms of the (negative) adsorption of one polymer by the other.

Hydrostatic pressure usually increases the glass transition temperature T_g of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in T_g with pressure as the polymer is plasticized by the environment. Just such a minimum in the T_g of polystyrene (PS) is observed as the pressure of CO₂ gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time‐temperature‐pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and T_g reach minima, at a CO₂ pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO₂. At the minimum, T_g is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO₂ at the lower temperature. The plasticization effect due to CO₂ can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO₂ gas is a severe plasticizer for polystyrene.

The degree of swelling and attendant reduction in the glass transition temperature have been determined for a 70% styrene–30% acrylonitrile copolymer in a large number of organic liquids. The critical strain ϵ_c for crazing or cracking has been determined also in air and in each agent. Limited crazing data have been obtained also on a dicyano bisphenol polycarbonate in which the CN groups take the place of the methyl groups in bisphenol A (BPA) polycarbonate. The two resins are compared with polystyrene and BPA polycarbonate, respectively, in terms of crazing resistance, swelling, and other properties. In both systems CN incorporation raises ϵ_c (air) and reduces susceptibility to liquids of low solubility parameter δ; T_g and shear yield stress are raised in the polycarbonate but not in the styrene system. The volume efficiency of CN in raising ϵ_c (air) is greater in the polycarbonate system than the styrene system; for the rise in polymer solubility parameter, CN efficiency is apparently reversed. These changes are discussed in terms of the differences in molecular architecture of the two systems. For glassy polymers, ϵ_c (air) is shown to depend in semiquantitative fashion on polymer T_g, δ, and resistance to shear deformation.

The solubility of carbon dioxide in symmetric (dense) cellulose 2.4‐acetate has been measured at temperatures from 0 to 70°C and pressures up to 45 atm. The polymer samples were prepared by slowly drying asymmetric reverse osmosis membranes. The solubility isotherms can be described satisfactorily up to 60°C by the “dual‐sorption” model for glassy polymers. The model cannot represent the experimental data above 60°C, possibly because of a second‐order transition in the polymer between 60 and 70°C. An analysis of the dual‐sorption parameters and of the heats of solution and “hole filling” suggests that the polymer samples contained a relatively large volume of microcavities. Gas solution appears to occur predominantly in microcavities, a large fraction of the penetrant moleculers being immobilized or partially immobilized. The solubilities obtained in this work are compared with similar data computed from time‐lag measurements of other investigators, and the validity of the dual‐sorption model is examined for the present case.

Blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) exhibit complex melting behavior when crystallized at low undercoolings. Three crystals comprised of two different PVF₂ forms grow. Hoffman‐Weeks plots of the observed melting points T_m of these crystals versus crystallization temperatures are constructed. The lowest‐melting‐point species, the α form, shows a change in slope which is attributed to fewer head‐to‐head PVF₂ units trapped in the crystal at higher temperatures. Defect energies in the crystal due to these units are calculated to be from 6.3 to 10.3 kJ/mol. Estimating lamellar thicknesses from the slopes of the two regions gives much more reasonable values when the high‐temperature data are used. Removal of kinetic effects that lower the observed T_m by extrapolating the data to obtain T permits the thermodynamic interaction energy density B between the two polymers to be obtained. The low‐temperature α‐form data give B = −8.83 × 10⁶ J/m³. The high‐temperature α‐form data and the T of the γ‐form crystals both show B to vary from −5.40 × 10⁶ to −2.96 × 10⁷ J/m³ as the blend composition goes from 40.1 vol % to pure PVF₂.

Light scattering measurements were carried out on a linear polyethylene sample NBS 1475 in 1‐chloronaphthalene at 135 and 115°C to determine the weight‐average molecular weight, the second virial coefficient A₂, and the z‐average mean‐square radius of gyration. By use of these results, the system is analyzed in terms of the interpenetration function Ψ for A₂. Observed values of A₂ are rather large but the excluded volume is nevertheless relatively small. Such behavior seem to be similar to that of semiflexible polymers. The characteristic ratio C_n,LS as determined by light scattering is found to be almost twice the literature value of 6.7, which was obtained from viscosity measurements. This discrepancy is explained by comparing the theoretical value of the Flory viscosity parameter Φ at the nondraining limit with values calculated from the light scattering results.

The parameters in the Mark‐Houwink relationship, [η] = K′M̄_v^a, for linear polyethylene in 1‐chloronaphthalene and 1,2,4‐trichlorobenzene at 130°C have been estimated. They were found by measuring the limiting viscosity numbers of a series of fractions with molecular weights ranging from less than 10,000 to almost 700,000. The results are for 1‐chloronaphthalene, [η] =0.0555 M̄_v^0.684 (with a standard error of 0.0064 in K′ and 0.010 in a) and for 1,2,4‐trichlorobenzene, [η] = 0.0392M̄_v^0.725 (with a standard error of 0.00703 in K′ and 0.015 in a), where [η] is expressed in ml/g. The unperturbed end‐to‐end distance calculated from the viscosity‐molecular weight data agrees with the theoretically expected value.

Properties of linear polyesters based on azoxybenzene and 2,2′‐methylazoxybenzene moieties with linear, flexible spacers based on mixtures of dodecanedioic acid (DDA) and methyladipic acid (MAA), chiral or racemic, of various compositions (system MAA/DDA‐8 and MAA/DDA‐9, respectively) have been described. Substitution of methyl groups in the 2,2′ or 3,3′ positions of the mesogenic core leads to soluble and relatively low‐melting‐point polyesters. The viscosity law for (MAA/DDA‐9) polyesters in 1,1,2,2 tetrachloroethane gives an exponent 0.76, indicating well‐sol‐vated, coiled chain conformations in dilute solution. Calorimetric data show an increase in isotropization entropy ΔS_NI with increasing average length of the spacer. This suggests a nonrandom conformation of the spacer in the nematic melt with a degree of order superior to that of low‐molecular‐weight analogs. X‐ray data obtained with an oriented nematic glass quenched from the nematic melt of DDA‐9 subjected to a magnetic field of 10–12 T also support the extended‐chain model in the nematic phase of DDA‐9. Oriented fibers can be produced by subjecting nematic melts of polyesters 8 and 9 either to magnetic fields of high intensity or to shear fields. The x‐ray data obtained from these fibers also support the extended‐chain model. Cholesteric systems do not orient in the magnetic field of 10–12 T. The study of mesophases of systems 8 and 9 indicates a dramatic influence of the position of the ester group on the stability of the mesophase in the azoxybenzene polyesters. The results are interpreted in terms of geometric factors influencing the colinearity of the mesogenic core and of the extended spacer.