This paper describes an in situ carbon-13 NMR study of the kinetics and mechanism of the functionalization of poly(methyl acrylate) (PMA) by reactions with various amines; While the reaction with n-hexylamine (HAN) in a binary solvent of dimethyl sulfoxide/o-dichlorobenzene (1:1, w/w) shows an autoacceleration effect, that with cyclohexanemethylamine (CN) exhibits autoretardation. The former is attributed to interactions that result in preferential solvation of nonpolar regions within the polymer domain, while the latter reflects the overwhelming effects of steric hindrance. Interestingly, while the presence of a single neighboring benzylamide group retards the reaction of benzylamine (BZA) with a PMA ester group, attach at an ester group flanked by benzylamide groups on either side is autoaccelerated. For the PMA partially functionalized with HAN the sequence distributions of the BAA and BAB triads, where A represents the unreacted ester and B the amide group, are in good agreement with the predictions of the neighboring-group model, but that of the AAA triads deviates systematically from the theoretical value. In contrast, the experimental values of unreacted monomer sequence distributions for PMA partially functionalized with CN deviate significantly from the theoretical predictions. These deviations are probably due to non-neighboring-group effects and/or the side reactions that accompany the functionalization process.