A copolymer comprising: a) 70 to 95 % by weight, based on the total weight of the copolymer, of monomer units derived from an acrylate of formula, wherein R 1 means a linear or branched alkyl group having from 4 to 18 carbon atoms and is selected from the group consisting of a C 4 linear alkyl group, a C 6 -C 10 linear alkyl group, a C 8 -C 18 branched alkyl group, a C 11 -C 18 linear alkyl group or a mixture thereof, and wherein the monomer units derived from the acrylate of formula are selected from 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 4 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 6 -C 10 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 8 -C 18 branched alkyl group; 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 11 -C 18 linear alkyl group; or a mixture thereof, based on the total weight of the copolymer, b) 5 to 30 % by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula, wherein R 2 means a linear alkyl group having from 2 to 4 carbon atoms, and wherein the copolymer has a weight-average molecular weight from 5,000 to 35,000 g/mol according to DIN 55672-1. a) 70 to 95 % by weight, based on the total weight of the copolymer, of monomer units derived from an acrylate of formula, wherein R 1 means a linear or branched alkyl group having from 4 to 18 carbon atoms and is selected from the group consisting of a C 4 linear alkyl group, a C 6 -C 10 linear alkyl group, a C 8 -C 18 branched alkyl group, a C 11 -C 18 linear alkyl group or a mixture thereof, and wherein the monomer units derived from the acrylate of formula are selected from 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 4 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 6 -C 10 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 8 -C 18 branched alkyl group; 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 11 -C 18 linear alkyl group; or a mixture thereof, based on the total weight of the copolymer, wherein R 1 means a linear or branched alkyl group having from 4 to 18 carbon atoms and is selected from the group consisting of a C 4 linear alkyl group, a C 6 -C 10 linear alkyl group, a C 8 -C 18 branched alkyl group, a C 11 -C 18 linear alkyl group or a mixture thereof, and wherein the monomer units derived from the acrylate of formula are selected from 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 4 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 6 -C 10 linear alkyl group; 0 to 95 % by weight of an acrylate of formula wherein R 1 is a C 8 -C 18 branched alkyl group; 0 to 45 % by weight of an acrylate of formula wherein R 1 is a C 11 -C 18 linear alkyl group; or a mixture thereof, based on the total weight of the copolymer, b) 5 to 30 % by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula, wherein R 2 means a linear alkyl group having from 2 to 4 carbon atoms,