Stationary and time‐resolved electron spin resonance spectroscopy measurements are employed to investigate the kinetics of the surface‐initiated reversible addition fragmentation chain transfer (RAFT) polymerization of n‐butyl acrylate from silica nanoparticles using both R‐ and Z‐group‐attached trithiocarbonates as RAFT agents. The obtained kinetic parameters reveal that the addition rate coefficient in the main equilibrium of RAFT graft polymerizations is significantly smaller than the one for comparable RAFT polymerizations in solution phase, as translational diffusion of surface‐attached molecules is limited. In comparison to the R‐group approach, the equilibrium constants of the Z‐group approach are about one to two orders of magnitude smaller due to a stronger shielding of the RAFT moieties.