Nitroxide-Mediated Copolymerization of MMA with Styrene: Sequence Analysis of Oligomers by Using Mass Spectrometry

The application of a sterically hindered alkoxyamine initiator for the nitroxide-mediated copolymerization (NMP) of methyl methacrylate (MMA) and styrene is presented. Working under the assumption that addition of a styrene monomer as the last embedded monomer of each dormant nitroxide-terminated copolymer will bypass the β-H-transfer (disproportionation, hydroxylamine elimination) that leads to termination of the living polymerization as observed for MMA polymerization, we successfully developed a method for the sequence analysis of oligomers by applying ESI mass spectrometry by using an orbitrap. With this method we were able to analyze chain end composition. To learn about the mass spectrometry fragmentation behavior of these nitroxide-terminated copolymers, we first analyzed different homo-oligomers and then went on with examples of co-oligomers. Oligomers consisting of styrene, n-butyl acrylate, and N-isobutylacrylamide (NIPAM), copolymers prepared from MMA and styrene, and alternating co-oligomers prepared from maleic acid anhydride and styrene were investigated. With the premise that oligomers containing 5−10 monomers are representative models for high molecular weight polymers, we could prove the validity of the assumptions made above.