Oxazine Ring-Related Vibrational Modes of Benzoxazine Monomers Using Fully Aromatically Substituted, Deuterated, ¹⁵N Isotope Exchanged, and Oxazine-Ring-Substituted Compounds and Theoretical Calculations

Abstract

Polymerization of benzoxazine resins is indicated by the disappearance of a 960-900 cm band in infrared spectroscopy (IR). Historically, this band was assigned to the C-H out-of-plane bending of the benzene to which the oxazine ring is attached. This study shows that this band is a mixture of the O-C stretching of the oxazine ring and the phenolic ring vibrational modes. Vibrational frequencies of 3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-a) and 3-(tert-butyl)-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-t) are compared with isotope-exchanged and all-substituted compounds. Deuterated benzoxazine monomers, N-isotope exchanged benzoxazine monomers, and all-substituted benzoxazine monomers without aromatic C-H groups are synthesized and studied meticulously. The various isotopic-exchanges involved deuteration around the benzene ring of phenol, selective deuteration of each CH in the O-CH-N (2) and N-CH-Ar (4) positions on the oxazine ring, or simultaneous deuteration of both positions. The chemical structures were confirmed by H nuclear magnetic resonance spectroscopy (H NMR). The IR and Raman spectra of each compound are compared. Further analysis of N isotope-exchanged PH-a indicates the influence of the nitrogen isotope on the band position, both experimentally and theoretically. This finding is important for polymerization studies of benzoxazines that utilize vibrational spectroscopy.

Synthesis and thermally induced structural transformation of phthalimide and nitrile-functionalized benzoxazine: toward smart ortho-benzoxazine chemistry for low flammability thermosets

“…37 Furthermore, the characteristic oxazinerelated mode is located at 938 cm À1 . 38 The FT-IR spectrum further supports the structure of the oPP-an obtained.…”

Bioinspired Design Provides High‐Strength Benzoxazine Structural Adhesives

“…[35] This peak was absent in the absorbance spectrum of cured B-a.Fourier transform infrared (FTIR) spectroscopic analysis of cured samples revealed ad isappearance of characteristic peaks affiliated with the oxazine ring at 940, 947 and 946 cm À1 for B-a, 2e and 1e, respectively,d enoting effective ring-opening polymerization (Figures S30-S32). [36] High-resolution XPS analysis of C1s and O1s peaks for B-a and 2e before and after curing corroborated this result ( Figures S39 and S40). Furthermore, the carbonyl content in thermoset 2e increased in both C1s and O1s high resolution XPS spectra, verifying the partial oxidation of catechol moieties to o-quinones during thermoset curing.…”

Design of thermosetting polymeric systems based on benzoxazines modified with maleic anhydride

“…The absorbance intensities at 3420 and 2960 cm − 1 corresponding to the stretching vibrations of hydroxyl and CH 2 groups are respectively observed, as well as the characteristic bands at 1500, 1260, and 935 cm − 1 attributed to the benzoxazine ring are detected . The band at 935 cm − 1 is related to the CO stretching of the oxazine ring and the phenolic ring vibrational modes, but it is mainly associated to oxazine ring . Moreover, the absorbance intensities at 1260 and 1500 cm − 1 are attributed to the asymmetric COC stretching and to the tri‐substituted benzene ring, respectively .…”

“…Figure (a) shows the evolution of the synthesis of BzPFA followed by 1 H‐NMR during the addition of maleic anhydride, dropwise with a syringe. The characteristic signals attributed to the benzoxazine structure, Ar CH 2 N and O CH 2 N are observed at 3.92 and 4.77, respectively . These signals decrease along the synthesis due to the formation of different oligomeric structures.…”