Phase transfer catalyzed reactions are often more easily and cheaply performed than conventional method and they are therefore of particular interest. A polysulfone functionalized with phosphonate (2-PSF) was prepared under phase transfer catalysis (PTC) conditions, and it was evaluated by spectrometric method (Fourier transform infrared spectroscopy, using potassium bromide (KBr) pellet). The phosphorus content of the modified polysulfone was determined, and it was used for the determination the fraction of repeating units functionalized with phosphonate groups. The modified polysulfone contains 1.40 mmol phosphonate/g polysulfone. Polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde groups (3-PSF) were used in Wittig-Horner reaction, to introduce double bonds on polymer and to obtain crosslinked polysulfone (4-PSF). The reactions were performed using PTC method, solid-liquid (potassium carbonate (K2CO3), tetrahydrofuran (THF), tetraethylammonium iodide (TEAI)) system. The structure of polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde group were confirmed by 1H-, 13C-, and 31P-nuclear magnetic resonance (NMR). The peak for phosphorus in PSF-phosphonate appears in 31P NMR spectrum as a singlet at 25.712 ppm. The thermal properties of aldehyde, phosphonate, and crosslinked polysulfone were studied by thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG). Scanning electron microscopy images for polysulfone functionalized with phosphonate and crosslinked polysulfone are in concordance with nitrogen (N2) adsorption-desorption isotherms.POLYM. ENG. SCI., 2012. (C) 2011 Society of Plastics Engineers