Acrylic star polymers containing multifunctional monomers in the core

A soluble acrylic star polymer comprising

• (a) a crosslinked core consisting essentially of a polymer derived from one or more monomers, each having at least two groups, ##STR33## and (b) attached to the core, at least 5 arms comprising polymer chains derived from one or more monomers, each having one group. ##STR34## in each of which R is the same or different and is H, CH.sub.3, CH.sub.3 CH.sub.2, CN or CO.sub.2 R' and Z' is O or NR', wherein R' is C.sub.1-4 alkyl, wherein:
• at least 50% of the molecules of such star polymers have at least from 5 to 2,000,000 arms, wherein the ratio of the number of arms to the number of difunctional acrylic repeat units in the core is less than or equal to 1:1, and
• (c) wherein the soluble is defined as that nothing separates out from a solution of 1% weight of the star polymer in 99% solvent of toluene, glyme or tetrahydrofuran upon centrifuging at 17,000 rpm for 30 minutes.