A new dialdehyde monomer, 4,4'-(hexafluoroisopropylidine) bis(p-phenoxy) benzaldehyde, was prepared; it led to a number of novel poly-Schiff bases in reactions with different diamines, such as 4,4'-diaminidiphenyl ether, 4,4'-(isopropylidine) bis(p-phenoxy) dianiline, 4,4'-(hexafluoroisopropylidine) bis(p-phenoxy) dianiline, and benzidine. The polymers were characterized with viscosity measurements, nitrogen analyses, and IR and H-1 NMR spectroscopy. These poly-Schiff bases showed good thermal stability up to 491 degreesC for 10% weight loss in thermogravimetric analysis under air and high glass-transition temperatures up to 215 degreesC in differential scanning calorimetry. These polymers were soluble in a wide range of organic solvents, such as CHCl3, dimethylformamide (DMF), dimethyl sulfoxide, and 1-methyl-2-pyrrolidon (NMP), and were insoluble in toluene and acetone. Thin films of these polymers cast from DMF exhibited tensile strengths up to 38 MPa. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 383-388, 2001.