Addition-curable phthalonitrile-functionalized novolac resin

Abstract

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 (1H-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°C with a low viscosity from 0.4 to 4 Pa.s. DSC results showed PN resin can be cured at about 220°C via thermal polymerization of phthalonitrile groups. An ultrahigh curing temperature (such as 375°C) that was typical for the other phthalonitrile functional prepolymers was not necessary for this resin and 250°C was used as a maximum post-cure temperature to achieve the desired properties. Thermogravimetric analysis (TGA) showed T5% (temperature of 5% weight loss) of the final cured products in nitrogen was 448.7°C, and the char yield was 70.29% at 900°C. Furthermore, T5% of cured PN resin in air was 455.2°C, and the char yield in air was 34.48% at 700°C,revealing that the cured resin possessed excellent thermo-oxidative stability. Dynamic mechanical analysis (DMA) showed the inflection point of tan δ was 371.9°C. The excellent processability and thermal stabilities proved PN resin as a promising candidate for advanced composite matrices.