A graft polymer comprising: (A) a block copolymer backbone as a graft base, wherein said block copolymer backbone (A) is obtainable by polymerization of at least two monomers selected from the group of ethylene oxide, 1,2-propylene oxide, 1,2butylene -oxide, 2,3-butylene oxide, 1,2-pentene oxide or 2,3-pentene oxide, where said block copolymer backbone (A) has three or more alkylene oxide blocks; (B) polymeric sidechains grafted onto the block copolymer backbone (A), wherein said polymeric sidechains (B) are obtainable by polymerization of at least one vinyl ester monomer (B1), wherein the vinyl ester monomer (B1) comprises at least 50%, by weight of B1 monomers, vinyl acetate, wherein the polymer has an OG of greater than 0, wherein OG = a X EO + b X M n 2 − c X M n × SUB − d X M n + e X SUB + h X wherein: "M n " is the number average molecular weight of the block copolymer backbone (A); "EO" is the molar ratio of ethylene oxide moieties to total alkylene oxide moieties present in the backbone (A), wherein EO is in the range of from 0 to less than 1.00, "SUB" is the weight percentage, by weight of the polymer, of polymeric sidechains (B); "a X " is a coefficient and equals 7.06; "b X " is a coefficient and equals 5.63×10 -7 ; "c X " is a coefficient and equals 1.25×10 -3 ; "d X " is a coefficient and equals 7.03×10 -3 ; "ex" is a coefficient and equals 3.66; and "h X " is a coefficient and equals 16.3. (A) a block copolymer backbone as a graft base, wherein said block copolymer backbone (A) is obtainable by polymerization of at least two monomers selected from the group of ethylene oxide, 1,2-propylene oxide, 1,2butylene -oxide, 2,3-butylene oxide, 1,2-pentene oxide or 2,3-pentene oxide, where said block copolymer backbone (A) has three or more alkylene oxide blocks; (B) polymeric sidechains grafted onto the block copolymer backbone (A), wherein said polymeric sidechains (B) are obtainable by polymerization of at least one vinyl ester monomer (B1), wherein the vinyl ester monomer (B1) comprises at least 50%, by weight of B1 monomers, vinyl acetate, wherein the polymer has an OG of greater than 0, wherein OG = a X EO + b X M n 2 − c X M n × SUB − d X M n + e X SUB + h X wherein: "M n " is the number average molecular weight of the block copolymer backbone (A); "EO" is the molar ratio of ethylene oxide moieties to total alkylene oxide moieties present in the backbone (A), wherein EO is in the range of from 0 to less than 1.00, "SUB" is the weight percentage, by weight of the polymer, of polymeric sidechains (B); "a X " is a coefficient and equals 7.06; "b X " is a coefficient and equals 5.63×10 -7 ; "c X " is a coefficient and equals 1.25×10 -3 ; "d X " is a coefficient and equals 7.03×10 -3 ; "ex" is a coefficient and equals 3.66; and "h X " is a coefficient and equals 16.3. "M n " is the number average molecular weight of the block copolymer backbone (A); "EO" is the molar ratio of ethylene oxide moieties to total alkylene oxide moieties present in the backbone (A), wherein EO is in the range of from 0 to less than 1.00, "SUB" is the weight percentage, by weight of the polymer, of polymeric sidechains (B); "a X " is a coefficient and equals 7.06; "b X " is a coefficient and equals 5.63×10 -7 ; "c X " is a coefficient and equals 1.25×10 -3 ; "d X " is a coefficient and equals 7.03×10 -3 ; "ex" is a coefficient and equals 3.66; and "h X " is a coefficient and equals 16.3. <EOS>