Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

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

Polymerization of benzoxazine resins is indicated by the disappearance of a 960-900 cm^-1 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-C₂ 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, ¹⁵N-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 CH₂ in the O-CH₂-N (2) and N-CH₂-Ar (4) positions on the oxazine ring, or simultaneous deuteration of both positions. The chemical structures were confirmed by ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The IR and Raman spectra of each compound are compared. Further analysis of ¹⁵N 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 polymerization of benzoxazine molecules with electron-withdrawing group substitution and ring-opening polymerization

The synthesis of strong electron-withdrawing group substituted aromatic amine and phenol-based benzoxazines is hampered due to the poor solubility of the reactant. In this article, a simple methodology is presented to synthesize the strong electron-withdrawing groups substituted benzoxazine monomers from a solution method using a low-boiling polar solvent. In order to achieve this, we used formaldehyde as a reactant as well as a solvent, and the reaction was carried out for a longer time. Also, benzylaniline derivatives were successfully prepared through benzoxazine. The monomers were polymerized by using solution polymerization method using lithium bromide as a catalyst. The structure of the monomers and polymers was confirmed by Fourier transform infrared and nuclear magnetic resonance spectroscopy. The thermally activated polymerization of the monomers was evaluated by differential scanning calorimetry, and thermal properties of polymers were analyzed by thermogravimetric analysis.

A study on the chain propagation of benzoxazine

Variation of T_g with conversion of step polymerization, living chain polymerization and non-living chain polymerization of benzoxazine during the curing process.

Simple and low energy consuming synthesis of cyanate ester functional naphthoxazines and their properties

Naphthoxazines functionalized with a cyanate ester group are synthesized in high yield under moderate conditions, including room temperature synthesis, compared with general benzoxazine synthesis.

A study on the co-reaction of benzoxazine and triazine through a triazine-containing benzoxazine

To study the co-reaction of benzoxazine and triazine, a triazine-containing benzoxazine (P-tta) was prepared through nucleophilic substitution of 4-(2H-benzo[e][1,3]oxazin-3(4H)-yl)phenol (P-ap) with 2,4,6-trichloro-1,3,5-triazine.

A novel benzoxazine/cyanate ester blend with sea-island phase structures

A novel C-BOZ/BADCy blend with sea-island phase structures was successfully prepared via reaction-induced phase separation.

Synthesis of a phosphinated tetracyanate ester and its miscible blend with 4,4′-oxydianiline/phenol-based benzoxazine

A phosphinated tetracyanate ester (4) was prepared and applied to copolymerize with a 4,4′-oxydianiline/phenol-based benzoxazine (P-oda) to enhance the properties of P-oda thermoset.

Mechanical and dielectric properties of blends of dicyanate ester and bisphenol A-based benzoxazine

Bisphenol A-based benzoxazine (BOZ) was blended with cyanate ester (CE) to improve the properties of cyanate resin. The effects of the content of BOZ on the mechanical property and dielectric property of the blends have been investigated. The results show that a suitable addition of BOZ can enhance the impact strength and flexural strength as well as reduce the dielectric constant and the dielectric loss of CE. The mechanical properties are significantly improved when the content of BOZ is 10 wt%, and the dynamic mechanical analysis reveals that the cross-link density of the blend is lower than pure CE. Scanning electron microscopy analysis shows distinct characteristics of ductile fracture of the blends. In addition, the dielectric constant and the dielectric loss of modified system decreases, compared with the curing CE. The optimal addition amount of BOZ resin is 15 wt% for the dielectric properties. The blend of a suitable addition of BOZ still remains a good thermal resistance. All these changes in properties are closely correlated to the copolymerization between BOZ and CE.

A simple method to introduce phosphoester groups into a polybenzoxazine backbone as multifunctional modifiers

Phosphoester groups were conveniently introduced into benzoxazine monomers by chemical bonding through nucleophilic reaction of a benzoxazine ring with diethyl phosphite (DEP).

Reaction mechanism and synergistic anticorrosion property of reactive blends of maleimide-containing benzoxazine and amine-capped aniline trimer

Reaction mechanism and synergistic effect on anticorrosion for reactive blends of a maleimide-containing benzoxazine and aniline trimer have been explored.

Azopyridine-functionalized benzoxazine with Zn(ClO4)2form high-performance polybenzoxazine stabilized through metal–ligand coordination

Azopyridine-functionalized benzoxazine (PBZ) was prepared and then blended with zinc ion through metal–ligand coordination to form a high performance polybenzoxazine after thermal curing.