Polymeric fatliquor comprising a sulfited maleic diester, obtained by a method comprising the following steps: - reaction of fatty alcohols C6-C24 alkyl or C6-C24 alkenyl, or a fatty ethoxylated alcohol having the general formula R(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, or a fatty ethoxylated carboxylic acid having the general formula RCO2(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300, or a fatty ethoxylated amine having the general formula RN(C2H4O)mH(C2H4O)nH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300 and n varying from 2 to 300, or a fatty ethoxylated amine having the general formula RR'N(C2H4O)mH with R and R' = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, with maleic anhydride, in a molar ratio 1:0.7 - 1.3, at a temperature of 50 - 150°C, for from 1 to 5 hours, to obtain a first reaction product, - reaction of said first reaction product with a copolymer of PEG/PPG having the general formula HO(CH36O)m(CH2CH2O)nH with m varying from 2 to 300 and n varying from 2 to 300, in a molar ratio 1:0.7 - 1.3, at a temperature of 160°C - 350°C, for from 2 to 10 hours to obtain a second reaction product; - vacuuming said second reaction product at -0.1 to - 0.9 bar with respect to atmospheric pressure, for from 20 minutes to 4 hours, till obtaining an acidity of the forming maleic diester to be less than 5 mg KOH; - sulfitation of said second reaction product with a water solution containing from 20 to 80% sodium metabisulfite or sodium sulfite or sodium bisulfite or ammonium bisulfite or gas sulfite anhydride in a molar ratio 1:0.7 - 1.3 preferably 1:1, at a temperature of 50 to 100°C, for from 1 to 4 hours, so as to obtain a water solution or dispersion or emulsion of polymeric fatliquor type B (sulfited maleic diester, GRASSPOL B), having from 20 % to 90% of active substance. - reaction of fatty alcohols C6-C24 alkyl or C6-C24 alkenyl, or a fatty ethoxylated alcohol having the general formula R(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, or a fatty ethoxylated carboxylic acid having the general formula RCO2(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300, or a fatty ethoxylated amine having the general formula RN(C2H4O)mH(C2H4O)nH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300 and n varying from 2 to 300, or a fatty ethoxylated amine having the general formula RR'N(C2H4O)mH with R and R' = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, with maleic anhydride, in a molar ratio 1:0.7 - 1.3, at a temperature of 50 - 150°C, for from 1 to 5 hours, to obtain a first reaction product, fatty alcohols C6-C24 alkyl or C6-C24 alkenyl, or a fatty ethoxylated alcohol having the general formula R(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, or a fatty ethoxylated carboxylic acid having the general formula RCO2(C2H4O)mH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300, or a fatty ethoxylated amine having the general formula RN(C2H4O)mH(C2H4O)nH with R = C6-C24 alkyl or C6-C24 alkenyl and m varying from 2 to 300 and n varying from 2 to 300, or a fatty ethoxylated amine having the general formula RR'N(C2H4O)mH with R and R' = C6-C24 alkyl or C6-C24 alkenyl, and m varying from 2 to 300, with maleic anhydride, in a molar ratio 1:0.7 - 1.3, at a temperature of 50 - 150°C, for from 1 to 5 hours, to obtain a first reaction product, - reaction of said first reaction product with a copolymer of PEG/PPG having the general formula HO(CH36O)m(CH2CH2O)nH with m varying from 2 to 300 and n varying from 2 to 300, in a molar ratio 1:0.7 - 1.3, at a temperature of 160°C - 350°C, for from 2 to 10 hours to obtain a second reaction product; - vacuuming said second reaction product at -0.1 to - 0.9 bar with respect to atmospheric pressure, for from 20 minutes to 4 hours, till obtaining an acidity of the forming maleic diester to be less than 5 mg KOH; - sulfitation of said second reaction product with a water solution containing from 20 to 80% sodium metabisulfite or sodium sulfite or sodium bisulfite or ammonium bisulfite or gas sulfite anhydride in a molar ratio 1:0.7 - 1.3 preferably 1:1, at a temperature of 50 to 100°C, for from 1 to 4 hours, so as to obtain a water solution or dispersion or emulsion of polymeric fatliquor type B (sulfited maleic diester, GRASSPOL B), having from 20 % to 90% of active substance.