Preparation And Properties Of Phthalonitrile Polymer And Its Nanocomposites

Phthalonitrile-based polymers, as a member of high-performance and high-temperature polymers family, are increasingly utilized for aerospace and microelectronic applications because of their limited water absorption, high glass transition temperature, outstanding thermal and thermo-oxidative stability, excellent mechanical properties and superior flame retardancy properties. Synthesis of novel monomers to improve the comprehensive performance of phthalonitrile-based polymers has become one of the focuses in recent years.The superior properties of nanodiamond (ND) such as good abrasion resistance, low friction coefficient, high hardness, good thermal conductivity, excellent chemical and thermal stability, and many other outstanding properties, have paved way for their use in high-performance composite. Using ND to prepare phthalonitrile nanocomposite is possible to enhance the integrated performance of phthalonitrile polymers.In order to improve the dispersion of ND in polymer matrix, ND was modified with mixed concentrated acid (H2SO4:HNO3=3:1). Fourier transform infrared spectroscope (FTIR) and thermal gravimetric analysis (TGA) results indicated that carboxyl groups were successfully introduced onto the surface of the ND, and the thermal stability of carboxylated nanodiamond (ND-COOH) was better than untreated ND.Resorcinol-based phthalonitrile (R-CN) nanocomposites with various ND contents were prepared, and TGA and DMA were used to evaluate the thermal stability and glass transition temperature of phthalonitrile nanocomposites. DMA exhibited a high glass transition temperature (Tg) above430℃for all the composites.In this study, a traditional resorcinol-based phthalonitrile monomer and novel naphthyl-based phthalonitrile monomers were prepared from the reaction of4-nitrophthalonitrile (NPN) with naphthalenediol (2,7-dihydroxynaphthalene2,7-DHN,1,6-dihydroxynaphthalene1,6-DHN,1,5-dihydroxynaphthalene1,5-DHN) and were cured to form phthalonitrile polymers in the presence of4,4’-oxydianiline (ODA) by two steps: preparation of prepolymer and postcuring into polymer. Thermogravimetric analysis (TGA) showed that the phthalonitrile-based polymers exhibit excellent thermal along with long-term oxidative stability after being fully cured. The initial decomposition temperatures (Tid) are all higher than488℃in air and N2atmosphere, and the1,6-BDCN polymers can maintain their structural integrity when heated up to400℃for hours. The dynamic mechanical analysis (DMA) exhibited a high storage modulus (>3GPa) at room temperature and a high glass transition temperature (>470℃). The polymers possess a lower water absorption (3wt%) after soak in boiling distilled water for48hours. When fully cured, the phthalonitrile-based polymers exhibit extremely high Tg, display excellent thermal and thermo-oxidative properties, and show limited water absorption.Throughout the introduction of flexible aromatic ether chain to naphthyl-based phthalonitrile monomers, we prepared six new low-melting naphthyl-based phthalonitrile (LMNP) monomers and resins, and presented the processability, thermal stability and dynamic mechanical properties of the resins. The results indicate that the polymers show a fine processability (125-155℃), outstanding thermal properties with the high Tid (>465℃) and high weight retention of above75%at1000℃in N2, and high Tgs (>380℃).