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Intramolecular Hydrogen Bonding in Benzoxazines: When Structural Design Becomes Functional
Authors:Prof. Dr. Pablo Froimowicz  Kan Zhang  Prof. Dr. Hatsuo Ishida
Affiliation:1. Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, USA;2. Design and Chemistry of Macromolecules Group, Institute of Technology in Polymers and Nanotechnologies (ITPN), UBA-CONICET, School of Engineering, University of Buenos Aires, Buenos Aires, Argentina;3. School of Materials Science and Engineering, East China University of Science and Technology, Shanghai, China
Abstract:The future evolution of benzoxazines and polybenzoxazines as advanced molecular, structural, functional, engineering, and newly commercial materials depends to a great extent on a deeper and more fundamental understanding at the molecular level. In this contribution, the field of benzoxazines is briefly introduced along with a more detailed review of ortho‐amide‐functional benzoxazines, which are the main subjects of this article. Provided in this article are the detailed and solid scientific evidences of intramolecular five‐membered‐ring hydrogen bonding, which is supposed to be responsible for the unique and characteristic features exhibited by this ever‐growing family of ortho‐functionalized benzoxazines. One‐dimensional (1D) 1H NMR spectroscopy was used to study various concentrations of benzoxazines in various solvents with different hydrogen‐bonding capability and at various temperatures to investigate in detail the nature of hydrogen bonding in both ortho‐amide‐functionalized benzoxazine and its para counterpart. These materials were further investigated by two‐dimensional (2D) 1H–1H nuclear Overhauser effect spectroscopy (NOESY) to verify and support the conclusions derived during the 1D 1H NMR experiments. Only highly purified single‐crystal benzoxazine samples have been used for this study to avoid additional interactions caused by any impurities.
Keywords:benzoxazines  hydrogen bonds  polybenzoxazines  polymers  structure–  activity relationships  substituent effects
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