Curing reaction and properties of a kind of fluorinated phthalonitrile containing benzoxazine

Development of an Atomic-Oxygen-Erosion-Resistant, Alumina-Fiber-Reinforced, Fluorinated Polybenzoxazine Composite for Low-Earth Orbital Applications

An atomic-oxygen-erosion-resistant fluorinated benzoxazine resin and composite were developed. The benzoxazine resin, abbreviated as “BAF-oda-fu,” consists of four benzoxazine rings, and was synthesized from bisphenol AF (BAF), 4,4′-oxydianiline (oda), furfurylamine (fu), and paraformaldehyde. The resin was characterized by infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An analysis of the solvent-washed product showed a technical grade purity (>95%) and a yield of approximately 85%. Subsequent polymerization of the resin was successfully performed by heating step-wise and opening the benzoxazine rings to form a crosslinked network. Thermal analyses showed a melting temperature of 115 °C and polymerization temperature of 238 °C, both being characteristic values of benzoxazine monomers. The benzoxazine resin was also blended with polyoctahedral sisesquoxane (POSS) and reinforced with alumina fibers. The Tg of the resin, as determined by DMA of the composite, could reach as high as 308 °C when post-curing and the POSS additive were utilized. The low-Earth orbit atomic-oxygen erosion rate was simulated by an RF plasma asher/etcher. The atomic-oxygen resistance of poly(BAF-oda-fu) fell along an established trend line based on its fluorine content.

Study on properties of copolymers based on different types of benzoxazines and branched epoxy resins

Previous studies on linear epoxy (bisphenol A epoxy) resin/benzoxazine composites showed that with the addition of epoxy (EP) resin, the resulting copolymers exhibited an increased glass transition temperature ( Tg) ( Tg reached a maximum value at a specific content), improved flexural strength, lower heat resistance, and reduced tensile strength. Herein, branched EP resin (AG-80)/benzoxazine copolymers featuring novolac (N-box) and siloxane (Si-box) chains were prepared without any external curing agent. In both systems, the EP resin endowed the copolymers with an increased crosslinking density; however, Tg continued to increase with increasing EP content. In addition, the heat resistance of the copolymers gradually enhanced. Different types of benzoxazines have various effects on the properties of copolymers. In terms of mechanical properties, AG-80/N-box copolymers exhibited brittle fracture characteristics; with increasing EP content, the flexural strength of the copolymer decreased while the tensile strength increased. AG-80/Si-box copolymers exhibited ductile fracture characteristics, with gradual increases in flexural and tensile strengths. Furthermore, with increasing EP content, the molecular chain migration ability and network homogeneity of the AG-80/N-box copolymers decreased gradually. Alternatively, in the case of the AG-80/Si-box copolymers, the molecular chain migration ability remained unchanged and network homogeneity improved. Hence, the developed copolymers can be used as resin matrices for the fabrication of advanced composites.