Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual‐mode sorption and transport type, (3) dual‐mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual‐mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and dimethyl‐3,7‐diaminodibenzothiophene‐5, 5‐dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′‐oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF3)2 groups. © 1992 John Wiley & Sons, Inc.

A vapor phase synthesis of dimethyl carbonate (DMC) from carbon monoxide and methyl nitrite (MN) has been carried out over Pd/NaY catalysts at 383 K, DMC was produced in a good yield. The selectivity to DMC was [85% on the basis of consumed CO or MN. The by-products were dimethyl oxalate, methyl formate and dimethoxymethane. The catalytic properties CO 2, N 2 O, of Pd/NaY were investigated as a function of Pd content and calcination temperature. It was found that 1 wt.% Pd/NaY calcined at 473 K in air was the optimum catalyst for the present DMC synthesis. The oxidation state and dispersion of Pd in the Pd/NaY catalysts were characterized by EXAFS and XPS. It was revealed that in 1 wt.% Pd/NaY changed into Pd metal Pd(NH 3 ) 4 2c lusters during the catalytic reaction. Pd metal clusters/NaY showed a stable activity for the DMC synthesis even after 700 h. These results suggest that the cage structure of NaY and anchoring e †ects of protons suppress Pd metal sintering and stabilize very small Pd metal clusters in the zeolite cages during the reaction.

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