Five new methyl-substituted diaminoterphenylenes were prepared by palladium-catalyzed coupling of bisboronic acids and bromoaromatics. The methyl groups are introduced to hinder rotations around the aromatic rings and to create a large free volume. These diamines were polycondensed with 4,4＇-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and the imidization of the resulting polyamic acids was chemically completed by treating with acetic anhydride and triethylamine. The permeabilities and apparent diffusion coefficients of the pure gases He, H-2, N-2, O-2, CO2, and CH4 were measured in a time-lag apparatus at feed pressures below 1 bar. Apparent solubility coefficients and some selectivities for gases were calculated, and these data were discussed in the light of polyimides with comparable structures.