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

Abstract 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