New phosphinoylcarbodithioate RAFT agents bearing dicyclohexyl- and di(piperidin-1-yl)phosphinoyl substituents were prepared, and their activity in RAFT polymerization of styrene and n-butyl acrylate was compared to that of previously reported diphenyl and bis(N,N-dlisopropylamino) counterparts. Polymerizations were performed in deuterated solvent with quantitative P-31 and H-1 NMR monitoring. This approach allowed to study the polymer co chain-end fidelity as well as RAFT agent transformations during the initialization period. It was also successfully applied for the monitoring of the block copolymerization. RAFT agents with cyclohexyl and piperidin-1-yl substituents bonded to the phosphorus center exhibited a marked improvement in the polymerization control with an optimal compromise between overall kinetics and control over molar masses and dispersities along with a significantly enhanced omega chain-end stability during polymerization.