Acrylic star polymers containing single-and multi-functional monomers in the core

An acrylic star polymer comprising

• a. a crosslinked core comprising a polymer derived from a mixture comprising
• i. from a small but effective amount for the purpose of decreasing the crosslink density in the core to 99% by weight of one or more monomers, each having one group ##STR41## and ii. the balance one or more monomers, each having at least two groups, ##STR42## and b. attached to the core, at least 5 arms comprising polymer chains derived from one or more monomers, each having one group, ##STR43## 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,
• such arms being of 1 or more types, wherein:
• i. the polymer chains comprising one of the types of arms have the same or different molecular weight and are derived from the same or different monomers as the polymer chains comprising the others of said types of arms, and
• ii. the polymer chains comprising each type of arms have an arm polydispersity of 1.0 to 2.0, where said arm polydispersity is the weight average molecular weight divided by the number average molecular weight of the polymer chains of that type, and,
• said star polymers, comprising both core and arms of 1 or more types, have a molecular polydispersity of 1.0 to 2.0, wherein said molecular polydispersity is the weight average molecular weight divided by the number average molecular weight of the molecules.