The invention relates to specific copolymers obtainable by co-polymerizing at least the following monomers: •at least one bicyclic (meth)acrylate ester •at least one lower-alkyl (meth)acrylate •optionally, and preferably, at least one aromatic vinyl monomer; and •optionally other ethylenically unsaturated monomers, whereby the copolymer has a weight averaged molecular weight of from 100,000 to 10,000,000 D, determined using GPC-MALS techniques for a solution in THF at 40° C., as well as to the way to synthesize such copolymers and the use of such polymers to modify the rheology of a liquid in which they are soluble.