Controlled/living polymerization of methyl methacrylate using new sterically hindered imidazoline nitroxides prepared via intramolecular 1,3-dipolar cycloaddition reaction

ABSTRACT A series of imidazoline nitroxides with bulky spirocyclic moieties at the positions 2 or 5 of imidazole ring were synthesized using intramolecular 1,3‐dipolar cycloaddition in 2H‐imidazole 1‐oxides or 4H‐imidazole 3‐oxides with pent‐4‐enyl groups followed by isoxazolidine ring opening and oxidation. Capability of the nitroxides to control radical polymerization of methyl methacrylate (MMA) and styrene was investigated. For that purpose, alkoxyamines were synthesized from the aforementioned nitroxides and tert‐butyl α‐bromoisobutyrate. Homolysis rate constants of the alkoxyamines were measured and possible contributions of side reactions were quantified. Nitroxide‐mediated polymerization of styrene and MMA was studied using the alkoxyamines as initiators. MMA polymerization was found to proceed in controlled regime up to 55% of monomer conversion and the polymer obtained was able to reinitiate the polymerization of styrene. Quota of “living” chains estimated to reach 90%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 929–943 Polymethacrylates possess valuable physical properties and have a wide range of applications, including biomedical. However, their preparation by means of nitroxide‐mediated polymerization (NMP) is still demanding. The preparation and application of imidazoline nitroxides that are successful in NMP of methacrylates are presented. These nitroxides are efficient mediators of NMP of styrene. Their application in polymerization makes it possible to prepare the block copolymers pMMA‐b‐pSty with blocks of high purity.