Sulfonated poly(phthalazinone ether sulfone ketone)s (SPPESK) were used to prepare thin film composite (TFC) membranes having increased thermal stability, hydrophilicity and potentially improved fouling-resistance. TFCs were prepared from SPPESK having a degree of sulfonation (DS) 1.5 as the top selective layer coated onto polysulfone (PSF) or poly(phthalazinone ether sulfone ketone)s (PPESK) asymmetric support membranes. At room temperature and 0.25 MPa pressure SPPESK/PSF composite membrane rejections for 1000 ppm Na2SO4 and NaCl were 91 and 41%, respectively and solution fluxes were 30 and 35 kg m(-2) h(-1). A SPPESK/PPESK, TFC membrane had rejections for Na2SO4 and NaCl of 67 and 30%, respectively with similar solution fluxes. Another SPPESK/PPESK membrane had a rejection 63% for 100 ppm Clayton Yellow dye (CY, MW = 695) while the solution flux was 62 kg m(-2) h(-1). When the feed solution temperature increased from 20 to 120 degreesC, solution flux was increased four-fold and the rejection decreased by 14%. The properties of the membrane were almost unchanged from the original values after the membrane was heated at 130 degreesC for 1 h and then decreased to 20 degreesC.