Acrylic star polymers containing single- and multi-functional monomers in the core, made by group transfer polymerization

Claim 1

An acrylic star polymer consisting essentially of 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, up to 99% by weight of a monomer, each having one group ##STR38## polymerizable by a group transfer polymerization process, ii. the balance one or more monomers having at least two groups ##STR39## polymerizable by a group transfer polymerization process and b. attached to the core, at least 5 arms comprising polymer chains derived from one or more monomers polymerizable by a group transfer polymerization process, each such monomer having one group ##STR40## in each of which R is the same or different and is H, CH 3 , CH 3 CH 2 , CN or COR' and Z' is O or NR', wherein R' is C 1-4 alkyl, and, said polymer being made by a process comprising group transfer polymerization utilizing a polymerization initiator selected from the group consisting of tetracoordinate organosilicon, organotin and organogermanium initiators having at least one initiating site, and a catalyst suitable for group transfer polymerization, in which star polymer one or more functional groups are attached to the arms, core, or the arms and core.