Synthesis and application of a benzoxazine-type phosphorus-containing monomer on epoxy/benzoxazine copolymer: Thermal stability and compatibility with liquid oxygen

摘要

Alkene-terminated monofunctional benzoxazine monomer (A-BA) was synthesized using allylamine, phenol and paraformaldehyde. Subsequently, the phosphorous-containing benzoxazine monomer (PBA) was obtained through the addition reaction between 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and A-BA in toluene. Finally, epoxy/benzoxazine copolymer with chemically-bonded DOPO was prepared using the synthesized PBA as hardener of DGEBA. DMA results showed that polymer with the chemically-bonded DOPO possessed higher modulus and crosslink density than that with physical-blended DOPO. Thermal gravimetric analysis (TGA) showed that the epoxy/benzoxazine copolymer possessed much better thermal stability around 500 degrees C and the DOPO-containing epoxy/benzoxazine copolymer showed promoted behavior compared to the neat one. The char residue of the epoxy/benzoxazine copolymer revealed dense surface layer and unbroken original dimension which was in accordance with the TGA results and the phosphorous-rich cover was observed. The liquid oxygen (LOX) compatibility of the copolymers was evaluated through mechanical impact in accordance with ASTM D2512-95 which showed that the LOX compatibility of the epoxy/benzoxazine copolymers were better than the epoxy/amine ones and the epoxy/benzoxazine copolymer including PBA exhibited promoted stability in the impact test. The surface elemental composition of the specimen before and after mechanical impact was investigated by X-ray photoelectron spectroscopy (XPS) and increased oxidation state of phosphorus was observed which explained the mechanism of phosphorus on promoting the LOX compatibility of the copolymer. (C) 2018 Elsevier Ltd. All rights reserved.