A novel vinylpyridine-based phthalonitrile monomer, namely 2,6-bis[4-(3,4-dicyanophenoxy)styryl]pyridine (BCSP), was synthesized from 2,6-bis(4-hydroxystyryl)pyridine (BHSP) via a nucleophilic displacement of a cyano-substituent with 4-nitrophthalonitrile (NPN). The phthalonitrile resin was cured with 4-(aminophenoxy)phthalonitrile (APPH), and its curing behaviour was investigated by differential scanning calorimetry (DSC), exhibiting a low melting point of 92 °C and an outstanding processing window of about 146 °C. The chemical structures of the BCSP monomer and polymers were characterized by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance spectroscopy (NMR). Different post curing temperatures and times resulted in polymers with different crosslinking levels and subsequently influenced the performance of the resins. The prepared BCSP polymer showed a high storage modulus (2.9 GPa–1.8 GPa) between 30 and 400 °C, a high glass transition temperature (T_g > 400 °C), and excellent thermal and thermo-oxidative stabilities with weight retention of 95% at 524.2 °C along with low water uptake.

A monomer of fluorinated phthalonitrile, namely 4,4′-bis(p-perfluoro-phenol-(bis(p-phenol)propane-2,2-diyl)-p-oxy-diphthalonitrile) (PBDP), was synthesized by the nucleophilic substitution reaction of bisphenol A, decafluorobiphenyl and 4-nitrophthalonitrile. The structure of the monomer was characterized by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results indicated that the PBDP monomer was synthesized successfully. The monomer was cured in the presence of 4-(aminophenoxy)phthalonitrile (APPH) and the curing behaviour was investigated by differential scanning calorimetry (DSC), suggesting a low melting point of 96 °C and an excellent processing window (96–262 °C). Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) showed that the fluorinated phthalonitrile resin possessed outstanding thermal and thermo-oxidative stabilities as well as good mechanical properties. The glass transition temperature was >400 °C and the 5% thermal degradation temperature was 501 °C. When the frequency was 50 MHz, the dielectric constant and dielectric loss of the polymer were 2.84 and 0.007, respectively. The PBDP resin has ultra-low water absorption of 0.77% and 1.4%, when exposed to an aqueous environment for 50 days at 24 °C and for 24 h at 100 °C, respectively. The prepared PBDP resin with outstanding thermal stability and low dielectric constant is an ideal candidate for aerospace industries, and microelectronic and other electronic packaging materials.

Resorcinol-based phthalonitrile (R-CN)/nano-aluminum oxide (Al₂O₃) nanocomposites were prepared via a two-step approach. Firstly, Al₂O₃ was functionalized with nitrile groups on the surface of Al₂O₃ nanoparticles, which was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy (SEM). The effect of nano-Al₂O₃ particles on thermomechanical and flexural properties has been evaluated for different weight ratios ranging between 0% and 5%. Compared with pure nano-Al₂O₃, nitrile-functionalized Al₂O₃ (CN-Al₂O₃) particles showed a more significant enhancement effect on the properties of R-CN resin. The storage modulus of nanocomposite with 5 wt% CN-Al₂O₃ reaches 2679 MPa at 25°C, which is much higher than that of the pure R-CN resin. For 3 wt% CN-Al₂O₃-reinforced R-CN composites, it showed an increase of 54.84% in flexural strength and 21.48% in flexural modulus. SEM was employed to explore the fracture surface of composites. Micrographs of fracture surface analysis confirmed that the toughness of R-CN resin can be improved significantly by incorporating CN-Al₂O₃ nanoparticles.

A series of high-temperature phthalonitrile monomers with o, m, p-dihydroxybenzene isomers, namely, 1,2-bis(3,4-dicyanophenoxy) benzene (o-BDB), 1,3-bis(3,4-dicyanophenoxy) benzene (m-BDB) and 1,4-bis(3,4-dicyanophenoxy) benzene (p-BDB), were synthesized via a facile nucleophilic displacement of a nitro-substituent from 4-nitrophthalonitrile. The structures of the monomers were characterized by FTIR, ¹H NMR and WXRD. Curing behaviors of the monomers with 4,4′-diaminodiphenyl ether were recorded by DSC. The result shows that the processabilities of o-BDB and m-BDB are superior to p-BDB due to lower melting points and broader processing windows. The structures of the cured phthalonitrile polymers were characterized by FTIR and WXRD, and thermal stabilities were evaluated by TGA and all the polymers exhibit excellent thermal and thermal-oxidative stabilities. Dynamic mechanical analysis reveals that the polymers have high storage modulus and high glass-transition temperatures. Consequently, o-BDB and m-BDB polymers show more outstanding processability, thermal stability and mechanical properties than p-BDB polymers, which may be good candidates for high-temperature phthalonitrile polymers.