Reaction behavior of sterically hindered alpha-(substituted methyl)acrylic esters with tert-butoxy radicals studied by a nitroxide trapping techniques

摘要

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 alpha-(2-methyl-2-carbomethoxypropyl)acrylic (methyl methacrylate dimer (MMAD))and methyl alpha-(2,2,2-tri(carbomethoxy)ethyl)acrylate (M(TM)EA).It has been shown that the adduct radical derived from MMAD ndergoes beta-fragmentation and expels the 2-carbomethoxy-2-propyl radical.No fragmentation was detected in the case of M(TM)EA.Rate coefficients of tapping and beta-fragmentation of the tertbutoxy radical in the literture have enabled estimationso of absolute rate coefficients for additions of the tert-butoxy radical and the methyl radical to monomer,hydrogen abstration from monomer by the tert-butoxy radical,and beta-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 shindrance of the alpha-substituted.