Synthesis, curing mechanism, thermal stability, and surface properties of fluorinated polybenzoxazines for coating applications

The development of materials with high thermal stability and good hydrophobicity is important in the field of coatings. Fluorinated benzoxazines are good choices for coating applications; however, fundamental discussion among structure, curing mechanism, and properties is still scarce. Thus, a series of new fluorinated benzoxazines, including totally new meta-fluoroaniline-, ortho-fluoroaniline-, and para-fluoroaniline-based benzoxazine, is successfully synthesized. The effect of different substituted positions of fluorine atoms on the curing mechanism, thermal stability, and surface properties of polybenzoxazines is discussed in detail based on experimental and theory analysis. The structural and geometrical parameters were investigated by NMR (1H, 19F) and FTIR spectroscopy. The curing peak temperature of fluorine-substituted benzoxazines was found to be in order of meta-fluoroaniline benzoxazine (m-Bf, 235.9 °C) < para-fluoroaniline benzoxazine (p-Bf, 244.4 °C) < ortho-fluoroaniline benzoxazine (o-Bf, 262.7 °C). Furthermore, the density functional theory (DFT) was used for quantitative analysis to determine the effect of fluorine atom position on the curing mechanism of benzoxazine for the first time. Moreover, the thermal stability (at 10% weight loss temperature) for different cured polybenzoxazines was found to be in the order of m-Bf (323.4 °C) < o-Bf (289.1 °C) < p-Bf (255.5 °C), and the hydrophobicity was in the order of m-Bf (121.4°) < o-Bf (119.3°) < p-Bf (106.3°). Meanwhile, the coatings based on fluorinated polybenzoxazines also have shown excellent mechanical and anti-corrosion properties. In this paper, not only new benzoxazines that can be used as coatings and composites are provided, but a deep understanding of the relationship among structure, curing mechanism, and performance of fluorinated benzoxazines is got.Graphical abstractThree fluorinated benzoxazines were synthesized and corresponding curing mechanism, thermal stability and possible application were discussed and showed.