Synthesis, characterization, and curing behavior of carborane‐containing benzoxazine resins with excellent thermal and thermo‐oxidative stability

Abstract

Two benzoxazine precursors bearing carborane moiety (1 and 2) were designed and synthesized successfully by the Mannich reaction of corresponding carborane bisphenol (3 and 4) with aniline and formaldehyde in 1,4-dioxane. The obtained precursors were characterized by using multiple spectroscopic techniques including GPC, FTIR, 1 H NMR, 13 C NMR, and 11 B NMR. Nonisothermal DSC studies showed that precursor 1 owned lower apparent activation energies (E a ) than 2. The optimum curing processes of benzoxazine precursors were also obtained on the basis of DSC data. TGA analyses manifested that the incorporation of carborane moiety endowed the obtained benzoxazine resins (cured 1 and 2) with excellent thermal stability and unique thermo-oxidative stability. The T d data showed that the initial degradation of both cured 1 and 2 under nitrogen and air was postponed to some extent owing to the shielding effect of carborane moiety on adjacent organic fragments. At higher temperature three-dimensional polymer networks with B-O-B and B-C linkages were formed as chars by the reaction of carborane cage with atmospheric moisture, degradation products such as phenolic hydroxyl, and oxygen (under air). Under nitrogen this network hindered the motion of radicals formed at elevated temperature and thus inhibited further polymer degradation processes. While under air, the formed boron-rich networks could hardly be further oxidized into carbon dioxide so that the carborane-containing benzoxazine resins also showed very high char yields.Closo-carboranes (C 2 B 10 H 12 ), with an icosahedral geometry, are excellent building blocks for thermally stable polymers. 17 Carboranes could absorb energy like a kind of "power gauge" at high temperature owing to its "superaromatic" electronic structure. Besides, the large volume of three-dimensional cage endows carboranes with strong shielding effect on adjacent segments. Therefore, carboranes were incorporated into many traditional polymers to improve their thermal stability including polysiloxanes, 18-26 epoxy resins, 27,28 phenolic resins, 29,30 aromatic polymers, 31 etc. With the increasing appearance of new polymers, carboranes expanded their application fields such as dendrimers [32][33][34][35][36][37][38] and conjugated polymers with light-emission property. [39][40][41][42][43][44] Additional Supporting Information may be found in the online version of this article.

Dielectric and thermal behaviors of fluorine‐containing dianhydride‐modified polybenzoxazine: A molecular design flexibility

“…In Figure (a), the chemical structure of poly(BAF‐a) showed the important characteristics of absorption bands centered at 1198 cm −1 (CF stretching) and 1482 and 856 cm −1 . The bands are assigned to a tetra‐substituted benzene ring, which has led to the formation of a Mannich bridge linkage and phenolic hydroxyl groups . Moreover, the ring‐opening reaction of BAF‐a monomer upon thermal treatment can also be observed through the appearance of a broad peak at 3400 cm −1 , which is assigned to the phenolic hydroxyl group formation.…”

“…The first approach is the modification of the structure of benzoxazine monomers with the introduction of other functional units or other molecular moieties. This could be one effective method to enhance the properties of the resulting polybenzoxazine . Recently, fluorine‐containing benzoxazine resin (abbreviated as F‐1) synthesized by using bisphenol‐AF, 4‐(trifluoromethyl)aniline, and paraformaldehyde as reagents was investigated .…”

Synthesis and Ceramic Conversion of a New Organodecaborane Preceramic Polymer with High-Ceramic-Yield

“…The FT-IR spectra of pyrolysis residues at different temperatures are shown in Figure 5 . We can see an absorption peak at 2572 cm −1 attributable to the stretching vibration of B-H in the decaborane cage [ 20 , 21 ]. Stretching vibration peaks of C-H at 2933 cm −1 and 2858 cm −1 , C=C-H at 2996 cm −1 and B-H at 2572 cm −1 are weakened at 200 °C.…”

Synthesis and characterization of carborane‐containing polyester with excellent thermal and ultrahigh char yield

“…Owing to these distinctive properties, carboranes have been regarded as one of the most excellent organic groups to improve performance of organic polymers with remarkable thermal stability . Therefore, carboranes were incorporated into many traditional polymers to improve their thermal stability including epoxy resins, phenolic resins, polyurethanes, organic silicone polymers, benzoxazine resins, polyimides, and so forth.…”