The combination of in situ (1)H NMR and in situ (31)P NMR was used to study the nitroxide mediated copolymerization of styrene and n-butyl acrylate. The alkoxyamine MAMA-DEPN was employed to initiate and mediate the copolymerization. The nature of the ultimate/terminal monomer units of dormant polymer chains were identifiedand quantified by in situ 31P NMR. Simulations of the styrene and n-butyl acrylate copolymerization mediated by DEPN were investigated using the Predici software package. The rate coefficients of reversible deactivation of chains with n-butyl acrylate as the terminal unit were estimated via parameter estimation studies using Predici. Good correlations were obtained between experimental data and simulated data.