A continuously variable composition copolymer is prepared in a reaction system, by (a) providing a reaction vessel comprising a first monomer composition; (b) providing a feed vessel comprising a second monomer composition; (c) initiating a polymerization reaction in the reaction vessel; (d) continuing the polymerization reaction during the gradual addition of the second monomer composition from the feed vessel to the reaction vessel, wherein the gradual addition of the second monomer composition is performed such that the continuously variable composition copolymer is obtained; (e) maintaining the polymerization until at least 90% of the total monomer composition has been converted to the copolymer; wherein the copolymer has a weight average molecular weight from 10,000 to 1,000,000; wherein the copolymer is soluble in lubricating oil, wherein the monomers of the first monomer composition provided in the reaction vessel comprise at least 50% by weight of all the monomers used to prepare the copolymer.