The immobilization of reversible addition-fragmentation chain transfer (RAFT) agents on silica for surface-initiated RAFT polymerizations (SI-RAFT) via the Z-group approach was studied systematically in dependence of the functionality of the RAFT-agent anchor group. Monoalkoxy-, dialkoxy-, and trialkoxy silyl ether groups were incorporated into trithiocarbonate-type RAFT agents and bound to planar silica surfaces as well as to silica nanoparticles. The immobilization efficiency and the structure of the bound RAFT-agent film varied strongly in dependence of the used solvent (toluene vs. 1,2-dimethoxyethane) and the anchor group functionality, as evidenced by atomic force microscopy, transmission electron microscopy, dynamic light scattering, and UV/Vis spectroscopy. Surface-initiated RAFT polymerizations using functionalized silica nanoparticles revealed that grafted oligomers, which often occur in SI-RAFT, are not formed within the crosslinked structures that originate from the immobilization, and that RAFT-agent films that show less aggregation during the immobilization are more efficient during SI-RAFT in terms of polymer grafting density. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 103-113