New polyimides for gas separation. 1. Polyimides derived from substituted terphenylenes and 4,4 '-(hexafluoroisopropylidene)diphthalic anhydride

Five new methyl-substituted diaminoterphenylenes were prepared by palladium -catalyzed coupling of bisboronic acids and bromoaromatics. The methyl grou ps are introduced to hinder rotations around the aromatic rings and to crea te a large free volume. These diamines were polycondensed with 4,4'-(hexafl uoroisopropylidene)diphthalic anhydride (6FDA), and the imidization of the resulting polyamic acids was chemically completed by treating with acetic a nhydride and triethylamine. The permeabilities and apparent diffusion coeff icients 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 coe fficients and some selectivities for gases were calculated, and these data were discussed in the light of polyimides with comparable structures.