Addition-curable phthalonitrile-functionalized novolac resin

A novel addition-curable novolac resin with phthalonitrile groups (PN) was successfully synthesized by a simple nucleophilic substitution reaction between the novolac resin and 4-nitrophthalonitrile. The final product was characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectrometry, and proton nuclear magnetic resonance (H-1-NMR) spectroscopy. Processing capability and cure behavior of PN resin was investigated by rheometer and differential scanning calorimetry (DSC), respectively. Rheometric studies showed PN resin possessed a broad processing window between 140 and 225 degrees C with a low viscosity from 0.4 to 4 Pa.s. DSC results showed PN resin can be cured at about 220 degrees C via thermal polymerization of phthalonitrile groups. An ultrahigh curing temperature (such as 375 degrees C) that was typical for the other phthalonitrile functional prepolymers was not necessary for this resin and 250 degrees C was used as a maximum post-cure temperature to achieve the desired properties. Thermogravimetric analysis (TGA) showed T-5% (temperature of 5% weight loss) of the final cured products in nitrogen was 448.7 degrees C, and the char yield was 70.29% at 900 degrees C. Furthermore, T-5% of cured PN resin in air was 455.2 degrees C, and the char yield in air was 34.48% at 700 degrees C,revealing that the cured resin possessed excellent thermo-oxidative stability. Dynamic mechanical analysis (DMA) showed the inflection point of tan delta was 371.9 degrees C. The excellent processability and thermal stabilities proved PN resin as a promising candidate for advanced composite matrices.