Improving the curing process and thermal stability of phthalonitrile resin via novel mixed curing agents

High curing temperature (including post-curing temperature) and long curing time of phthalonitrile resins make them thermally stable but difficult to process. In this paper, novel mixed curing agents (CuCl/4,4′-diaminodiphenylsulfone (DDS) and ZnCl 2 /DDS) were firstly designed for solving these problems. Bisphenol-based phthalonitrile monomer (BP-Ph; melting point: 228–235 °C) was synthesized and used as the curing precursor. Differential scanning calorimetry results indicated that BP-Ph cured with CuCl/DDS and ZnCl 2 /DDS exhibited curing temperatures close to the melting point of BP-Ph with curing ending temperatures of 225.4 and 287.1 °C, respectively. Rheologic investigations demonstrated obvious curing reactions of BP-Ph occurred with the mixed curing agents at 220 °C. Thermogravimetric analysis showed that BP-Ph cured by CuCl/DDS or ZnCl 2 /DDS maintained 95% mass at 573 or 546 °C, respectively, at a post-curing temperature of 350 °C for 2 h. Reasonable long-term thermo-oxidative stability was also demonstrated. When the post-curing temperature decreased to 290 °C, char yield at 800 °C of BP-Ph cured by CuCl/DDS was 77.0%, suggesting the curing procedure can be milder when using mixed curing agents. © 2017 Society of Chemical Industry