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.

Sesamol and furfurylamine are used to synthesize a novel benzoxazine monomer as part of the quest to develop greener benzoxazine monomers simultaneously fulfilling two Principles of Green Chemistry, the use of renewable feedstocks and safer solvents and auxiliaries. Respecting principle 5, the so-called preferred solvents (ethanol and ethyl acetate) are used in both the syntheses and purification processes. The chemical structure of the synthesized monomer is verified by proton and carbon nuclear magnetic resonance spectroscopy (1H and 13C NMR), 2D 1H–13C heteronuclear single quantum correlation (HSQC) spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The polymerization behavior of the monomer and the thermal stability of fully polymerized polybenzoxazine are studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A thermally stable polymer has been obtained as shown by the 5% and 10% weight reduction temperature (T d5 and T d10) values of 374 and 419 °C, respectively, and a char yield of 64%, making this thermoset a promising candidate for fire-resistant applications.

The majority of the published bio-based benzoxazine research has focused almost exclusively on different phenolic and amine compounds, while the aldehyde portion of the oxazine ring remains the same.

A systematic study has been carried out to develop a material with significant protection properties from galactic cosmic radiation and solar energetic particles. The research focused on the development of hydrogen-rich benzoxazines, which are particularly effective for shielding against such radiation. Newly developed benzoxazine resin can be polymerized at 120 °C, which meets the low-temperature processing requirements for use with ultrahigh molecular weight polyethylene (UHMWPE) fiber, a hydrogen-rich composite reinforcement. This highly reactive benzoxazine resin also exhibits low viscosity and good shelf-life. The structure of the benzoxazine monomer is confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. Polymerization behavior and thermal properties are evaluated by differential scanning calorimetry and thermogravimetric analysis. Dynamic mechanical analysis is used to study chemorheological properties of the benzoxazine monomer, rheological properties of the cross-linked polybenzoxazine, and rheological properties of UHMWPE-reinforced polybenzoxazine composites. The theoretical radiation shielding capability of the composite is also evaluated using computer-based simulations.

Photochemical reactions tend to give more than one photoproduct. However, such a reaction can be a powerful synthetic tool when it is possible to conduct it in regioselective conditions yielding a single photoproduct. Water-surfactant solutions as reaction media can be considered as an approach in this context because they show products with different features than those from isotropic solutions. Here we describe results obtained from studying the effect on the prototypical photoreaction, known as the photo-Fries reaction of several substituted acetanilides and α-naphthyl acetamide within surfactant micelles (ionic and non-ionic micelles). This reaction involves homolytic cleavage of a C-N bond to yield a singlet radical pair. The surfactant micelles control the rotational and translational mobility of the radical pair, resulting in noticeable photoproduct selectivity.

The pure monofunctional benzoxazines substituted by either electron donating or withdrawing groups are synthesized to verify the electronic effect on the polymerization behaviors without any complicated factors of the impurities.

Polybenzoxazines are a relatively new type of thermoset polymer that has primarily been used for the development of composite materials. However, there is an existing interest in expanding the applications for this family of polymers. One way of achieving this goal is by taking advantage of the molecular structure, where the presence of oxygen and nitrogen atoms with lone electron pairs allows the formation of coordination complexes and chelates between the benzoxazine oligomers and polymers with metal ions. This article is focused on studying the relationship between the spatial conformation of the polybenzoxazine and the capacity to form coordination complexes from a fundamental point of view as well as practical applications of this concept. Thus, it can be seen that use of polybenzoxazines for the removal of heavy metals from water and the use of benzoxazine dimers for the synthesis of CeO2 nanoparticles are examples of very different applications based on the same working principle.

No abstract