A process for producing a vinyl aromatic-conjugated diene block copolymer, the process comprising solution polymerising at least one vinyl aromatic hydrocarbon and a conjugated diene in the presence of a catalyst based on an alkali metal to produce copolymer chains which end with an alkali metal and treating the copolymer chains in solution with an alkyl dicarboxylic acid having at least 2 carbon atoms and the acid being in the form of a slurry in an organic liquid with the acid being granulated and having an average granule size of less than 50 microns.