Thermal and oxidative behavior of a tetraphenylsilane-containing phthalonitrile polymer

Abstract

Phthalonitrile polymers have potential for high-temperature applications in polymer matrix composites as electronic encapsulation compounds. To investigate the effect of inclusion of an organosilicon moiety, a tetraphenylsilane-containing phthalonitrile monomer was synthesized in high yields. The monomer possessed a high melting point of 222–223°C, while no hydrolytic sensitivity was observed. Cured polymers exhibited glass transitions in the range of 290–325°C and coefficients of thermal expansion of 73–77 µm/(m °C). In thermogravimetric analysis (TGA), 5 wt% loss was observed at 482–497°C and 519–526°C, under air and nitrogen, respectively. Infrared (IR)-TGA of evolved gases revealed multiple degradations in both nitrogen and air. The material possessed good thermo-oxidative stability (TOS) when aged in air at 250°C. After aging for 5000 h, oxidative degradation was characterized using Fourier transform IR microscopy, energy dispersive spectroscopy, optical microscopy, and Knoop hardness testing. Four zones were identified in aged samples. The cleavage of Si-phenyl bonds and the formation of Si–O phases and carbonyl groups were observed.

Effect of post‐curing temperature on the retention of mechanical strength of phthalonitrile thermosets and composites after a long‐term thermal oxidative aging

“…The temperature range has been chosen in order to determine the temperature limit of a long‐term application of the phthalonitrile resins under air atmosphere. Generally, the operation temperature must not exceed the post‐curing temperature or glass transition temperature of the matrix to avoid devitrification at the considered conditions 38,42,56 . According to this, the resin post‐cured at 330°C was aged in temperature range 280–330°C, and the resins post‐cured at 350°C and 375°C–in the range of 300–350°C.…”

“…Generally, the operation temperature must not exceed the post-curing temperature or glass transition temperature of the matrix to avoid devitrification at the considered conditions. 38,42,56 According to this, the resin post-cured at 330 C was aged in temperature range 280-330 C, and the resins post-cured at 350 C and 375 C-in the range of 300-350 C.…”

“…The long-term thermal oxidation was also reported in. 38 The mass loss of 13% was observed after 5000 h thermal aging at 250 C of phthalonitrile resins post-cured at 350 C for 4 hours along with crack penetration into the volume to a depth of 400-700 μm from the surface. The aged samples were studied via FTIR, EDS and Knoop hardness methods.…”

“…[33][34][35][36][37][38] The most common method of thermal and thermal oxidative stability evaluation is non-isothermal TGA method corresponding to short-term stability 37,[39][40][41] but there are not a lot of works concerning long-term isothermal oxidative stability of phthalonitrile resins. 38,[42][43][44] The reported results of TGA studies revealed a valuable data related to the products of phthalonitriles degradation. For example, in reference 38 it was found that the thermal degradation of phthalonitrile resins under inert atmosphere is a multi-stage process with release of such volatile products as hydrogen cyanide and nitrogencontaining aromatic compounds, including plausibly isoindoline structures at the first stage (Tp = 540 C), benzene-at the second stage (Tp = 580 C), ammonia and hydrogen cyanide-at the third (Tp = 610 C) and fourth (Tp = 700 C) stages.…”

Polymerization mechanism of 4-APN and a new catalyst for phthalonitrile resin polymerization

“…At present, researchers basically believe that CN polymerization mainly produces triazine, isoindole and phthalocyanine rings, [31][32][33][34][35][36][37][38][39][40][41][42] does not produce small molecules, and gives the polymerization mechanism of forming the three heterocycles. However, this does not explain the experimental results in this paper very well.…”