Addition-curable phenolic resin with arylacetylene groups: preparation, processing capability, thermal properties, and evaluation as matrix of composites

Ethynyl phenyl azo novolac resin with substitution extent of 100% (EPAN100) was synthesized by a two-step procedure, including coupling reaction between salicyl alcohol and diazonium sulfate of 3-ethynyl aniline to get 4-(3-ethynylphenyl) azo salicyl alcohol (EPAS), and its polycondensation reaction. EPAS and EPAN100 were characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy ((1)H-NMR), and gel permeation chromatography. The melt viscosity characteristics of the resin were investigated by TA AR2000 rheometer. The cure characteristics and cure schedule of EPAN100 were determined by differential scanning calorimetry (DSC) analysis and the FT-IR technique. The DSC curve of EPAN100 showed a cure exotherm between 120 and 280 degrees C with an enthalpy of 416 J g(-1), which was far lower than that of 1079 J g(-1) for polyarylacetylene resin (PAA). Dynamic mechanical analysis and thermal gravimetric analysis were used to investigate the thermal stability of EPAN100. The results showed that cured EPAN100 resin possessed significantly improved thermal stability and char-yielding property relative to novolac-type phenolic resin. The onset decrease temperature of storage modulus (T(onset)) and glass transition temperature (T(g)) were 350 and 400 degrees C, respectively. The 5% weight loss temperature (T(d)(5)) was approximately 420 degrees C, and the char yield at 900 degrees C in nitrogen was approximately 79%. In comparison with PAA-matrix composites, the composites of EPAN100 resin presented much higher mechanical strength both at room and high temperature. Scanning electron microscope analysis showed that silica cloth/EPAN100 resin possessed better interaction between resin and fibers.