Synthesis, thermal properties, and ceramization of a novel ethynylaniline-terminated polysilazane

Abstract

A novel ethynylaniline-terminated polysilazane (PCSN) was synthesized from the ammonolysis reaction of dichloromethylsilane (MeSiHCl2) and p-phenylenediamine, by which terminal ethynyl groups were introduced into the resultant PCSN. Different average molecular weight PCSNs obtained with adjusting the molar ratios between p-phenylenediamine and MeSiHCl2 were used to investigate the influence of average molecular weights and contents of terminal ethynyl groups on thermal properties and ceramic conversions of PCSNs. The structure of PCSN was characterized using Fourier transform infrared, proton, carbon-13, and silicon-29 nuclear magnetic resonance spectroscopies. Among all the PCSN precursors, PCSN-4 has the lowest curing temperature (237.1°C) and the highest enthalpy (863.0 J g−1) because of its highest content of terminal ethynyl groups, improving its cross-linking. The thermal properties of cured PCSN were studied by means of thermogravimetric analysis under nitrogen atmosphere. The collaborative effect from both the average molecular weight and the contents of terminal ethynyl groups gave PCSN-3 the best thermal stability. The temperature of 5% mass loss was 564°C and the residual mass at 900°C was 84.4%. After sintering at 1450°C in argon atmosphere, PCSN-3 thermoset turned into black solids composited of β-silicon carbide (β-SiC), α-silicon nitride, α-SiC, and free carbon with a yield of 78.4%, indicating PCSN had the potential to be used as ceramic precursors.