The invention relates mainly to a polymer comprising a hydrocarbon-based main chain bearing carboxylic groups and polyalkoxylated chains and up to 4% by weight of anti-oxidant groups, relative to the weight of the final polymer, grafted to the main chain. It also relates to a method for preparing such a polymer and to an admixture which is of use as a plasticizer of suspensions of mineral particles comprising same. Finally, it is related to the use of such a polymer for fluidifying suspensions of mineral particles and reducing the water demand of hydraulic compositions.