Nitroxide‐Mediated Polymerization of Methyl Methacrylate Using an SG1‐Based Alkoxyamine: How the Penultimate Effect Could Lead to Uncontrolled and Unliving Polymerization

Summary: The nitroxide‐mediated polymerization (NMP) of MMA initiated with a new crowded SG1‐based alkoxyamine was performed. Contrary to the results expected after a kinetic analysis (Fischer's diagram), the polymerization of MMA at 45 °C with SG1 showed only partial control and livingness during the first 15% of conversion. Simulations using PREDICI highlighted that the kinetic rate constants currently in use had not been correctly estimated and that a strong penultimate effect drastically increased the equilibrium constant K (7 × 10 −7 ), preventing a well‐controlled polymerization. Experimental determination of the k c value (1.4 × 10 4 L · mol −1  · s −1 ) confirmed a strong penultimate effect on the recombination reaction, whereas for the dissociation reaction this effect is lower ( k d  = 10 −2  · s −1 ).Nitroxide‐mediated polymerization of MMA at 45 °C initiated with a new crowded SG1‐based alkoxyamine.