A novel thermoresponsive shell crosslinked three-layer onion-like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (-SC(S)S-) first; then, it was used as chain transfer agent to prepare star-like block copolymer of N-isopropyl acrylamide (NIPA) and N,N-dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three-layer polymer, PG-[SC(S)S-(DMA)-b-(NIPA)](n), was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8-diiodoctane, and the resulting onion-like three-layer polymer showed a lower critical solution temperature (LOST) in water because of the outer layer of poly(NIPA). The LOST value only slightly depended on the crosslinking degree. Finally, the -SC(S)S- were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. (c) 2005 Wiley Periodicals, Inc.