The invention concerns a polymer derived from a polysaccharide copolymer consisting of a main chain comprising several similar or different anhydrohexose units, and branches comprising at least a neutral or anionic anhydropentose and/or anhydrohexose unit; said polymer derivative comprising one or several units bearing an oxime function at least on position C2. Furthermore, the polymer is obtainable by carrying out the following steps: a) contacting a polysaccharide with an aqueous solution comprising at least an oxidising agent for oxidising at least the hydroxyl radical borne by the carbon C2 of one or several units, into a ketone function; b) contacting the resulting polymer with hydroxylamine or a derivative to transform the ketone function into an oxime function. The invention also concerns a polymer obtainable by carrying out a step c) which consists in contacting the polymer having at least an oxime function at least on position C2 of said unit, with an agent reducing the oxime function. The resulting polymer bears an amine function at least on position C2. The invention further concerns the uses of said polymers.