AbstractPolysulfone has been carboxylated, via a metalated intermediate, by reaction of a THF solution of polymer with n‐butyllithium and then treatment with carbon dioxide. The polymer reactions with n‐butyllithium were close to quantitative and did not require the use of a tertiary amine catalyst. A series of polymers ranging from 0.2 to 1.9 carboxyl groups per repeat unit was prepared by this method in the salt, acid and ester form. The structures of these polymer derivatives were characterized by 1H‐NMR, 13C‐NMR and IR. The glass transition temperatures and thermal stabilities were characterized by differential scanning calorimetry (DSC) and thermogravimetry (TG).