A series of phenylethynyl (PE)-end-capped cooligomides with number-average molecular weights (M-n) of 4000 and 7000 based on 4,4'-(hexafluoroisopropylidene)dipthalic anhydride (6FDA) and para- and meta-phenylene diamines containing 80/20 and 70/30 p/m molar ratios in the repeat unit were synthesized and characterized for their thermal and rheological properties. The cooligomides with M-n = 7000 exhibited high melt viscosities with respect to the cooligomides with M-n = 4000 at both 80/20 and 70/30 p/m molar ratios. PE-end-capped cooligomides with M-n = 4000 based on 4,4'-(2,2,2-trifluoro-1-phenylethylidene)dipthalic anhydride (3FDA) and para- and meta-phenylene diamines containing 80/20 and 70/30 p/m ratios in the repeat unit were also investigated. The PE-6FDA cooligomide, blended with 3,4'-bis(phenylethynyl)phthalimido diphenylether, exhibited lower viscosities than unblended cooligomides. However, a blend of the 3FDA cooligomide and reactive diluents containing 3FDA exhibited a much lower viscosity than a blend of the 6FDA cooligomide and a reactive diluent containing 6FDA. (C) 2003 Wiley Periodicals, Inc.A series of phenylethynyl (PE)-end-capped cooligomides with number-average molecular weights (M-n) of 4000 and 7000 based on 4,4'-(hexafluoroisopropylidene)dipthalic anhydride (6FDA) and para- and meta-phenylene diamines containing 80/20 and 70/30 p/m molar ratios in the repeat unit were synthesized and characterized for their thermal and rheological properties. The cooligomides with M-n = 7000 exhibited high melt viscosities with respect to the cooligomides with M-n = 4000 at both 80/20 and 70/30 p/m molar ratios. PE-end-capped cooligomides with M-n = 4000 based on 4,4'-(2,2,2-trifluoro-1-phenylethylidene)dipthalic anhydride (3FDA) and para- and meta-phenylene diamines containing 80/20 and 70/30 p/m ratios in the repeat unit were also investigated. The PE-6FDA cooligomide, blended with 3,4'-bis(phenylethynyl)phthalimido diphenylether, exhibited lower viscosities than unblended cooligomides. However, a blend of the 3FDA cooligomide and reactive diluents containing 3FDA exhibited a much lower viscosity than a blend of the 6FDA cooligomide and a reactive diluent containing 6FDA. (C) 2003 Wiley Periodicals, Inc.