Permeability and solubility coefficients for H2, CO2, O2, CO, N2, and CH4 in polyimides prepared from 6FDA and methyl‐substituted phenylenediamines were measured to investigate effects of the substituents on gas permeability and permselectivity. The methyl substituents restrict internal rotation around the bonds between the phenyl rings and the imide rings. The rigidity and nonplanar structure of the polymer chain, and the bulkiness of methyl groups make chain packing inefficient, resulting in increases in both diffusion and solubility coefficients of the gases. Polyimides from tetramethyl‐p‐phenylenediamine and trimethyl‐m‐phenylenediamine display very high permeability coefficients and very low permselectivity due to very high diffusion coefficients and very low diffusivity selectivity, as compared with the other polyimides having a similar fraction of free space. This suggests that these polyimides have high fractions of large‐size free spaces.
Rheological properties of high and low density polyethylene melts (HOPE and LDPE) were measured under two different deformation modes: sinusoidal strain (“dynamic”) and constant rate‐of‐strain (“steady‐state”). For the sinusoidal measurements, a torsional geometry was used, whereas the “steady‐state” measurements were carried out in both torsional and capillary flow. The complex and “viscous” components of the “dynamic” viscosity were compared with the “steady‐state” viscosities, corrected for both non‐Newtonian and end effects. For the HDPEs, the Cox‐Merz rule was found to be not valid. The corrected viscosity is closer in magnitude to the “viscous” component, and not to the complex viscosity. However, for the LDPEs, the corrected viscosity is equivalent to the complex viscosity. These results are compared to other correlations found by various authors.
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