Two synthesis routes for the preparation of novel base-modified polysulfones (PSUs; Udel((R))) were investigated: (1) the addition of the basic aromatic ketones 2,2 ' -dipyridylketone and 4,4 ' -bis-(diethylamino)benzophenone and the basic aromatic aldehydes N,N-dimethylamino-benzaldehyde, pyridine-2-aldehyde, pyridine-3-aldehyde, and pyridine-4-aldehyde to lithiated PSU and (2) the reaction of lithiated PSU with basic aromatic carboxylic acid esters such as 4-N,N-dimethylaminobenzoic acid ethylester, pyridine-2-carboxylic acid ethylester, pyridine-3-carboxylic acid ethylester, and pyridine-4-carboxylic acid ethylester. Both synthesis routes lead to a high degree of conversion, without the occurrence of crosslinking. This is remarkable, especially for the reaction of lithiated PSU with the ester compounds, because the - (C=O)-Ar groups formed by the reaction of the ester with PSU-Li are not further converted with the remaining PSU-Li sites to (crosslinked) PSU-C(-OLi)-Ar-PSU alcoholates, as normally observed when esters are reacted with Li-organic compounds. Starting with dilithiated PSU, we obtained degrees of substitution of 0.8-2 groups per PSU repeating unit. The structures and compositions of the modified PSU polymers were confirmed with NMR spectroscopy and elemental analysis. The modified polymers were also characterized via thermogravimetric analysis (thermal stability). Interestingly, the product of the reaction of lithiated PSU with 4,4 ' -bis-(diethylamino)benzophenone could be oxidized to a deep blue polymeric dye that showed proton self-conductivity.