The nitroxide free radical trapping technique in connection with HPLC and electrospray ionization mass spectrometry has been employed to study reactions of tert-butoxy radicals with methyl -(2-methyl-2-carbomethoxypropyl)acrylate (methyl methacrylate dimer (MMAD)) and methyl -(2,2,2-tris(carbomethoxy)ethyl)acrylate (M(TM)EA). It has been shown that the adduct radical derived from MMAD undergoes -fragmentation and expels the 2-carbomethoxy-2-propyl radical. No fragmentation was detected in the case of M(TM)EA. Rate coefficients of trapping and -fragmentation of the tert-butoxy radical in the literature have enabled estimations of absolute rate coefficients for additions of the tert-butoxy radical and the methyl radical to monomer, hydrogen abstraction from monomer by the tert-butoxy radical, and -fragmentation of the adduct radical (MMAD only). The reactions of tert-butoxy radicals with M(TM)EA are slower than with MMAD due to the steric hindrance of the -substituent.