The present invention relates to a copolymer comprising units of type A deriving from carboxylic acid monomers and units of type B deriving from sulfonic acid monomers, said units of type A and B representing more than 80 mol % of the total moles of units in the copolymer, characterized in that it comprises at least: —one first block formed of at least 95 mol % of units of type A and having a degree of polymerization DP1 comprised between 5 and 150; and —one second block formed of at least 95 mol % of units of type A and B with a molar ratio of units of type A to units of type B greater or equal to 1, wherein said units of type A and units of type B are statistically distributed, said second block having a degree of polymerization DP2 such that DP2/DP1≧1. It also relates to new detergent compositions comprising such a copolymer, and to the use of this copolymer in a detergent composition, especially an ADW composition, to prevent, limit or eliminate the filming phenomena.