Synthesis and characterization of novel silazane-modified amine curing agents for enhanced thermo-mechanical properties in epoxy resins

In this study, two novel silazane-modified amine curing agents, MeSZ-1 (fatty amine-modified) and MeSZ-2 (aromatic and fatty amine-modified), were synthesized from methylsilazane (MeSZ) via ammonolysis of chlorosilanes followed by grafting with ethanolamine and 4-aminophenol. The structures were characterized using Fourier-transform infrared (FTIR) spectroscopy, confirming the formation of Si-O bonds and retention of residual Si-N bonds, with proposed oligomeric architectures incorporating cyclic and branched segments. These agents were employed to cure bisphenol A epoxy resin, and their performance was benchmarked against conventional curing agents: polyetheramine D230 (aliphatic) and diethyltoluenediamine (DETDA, aromatic). Mechanical evaluations, including tensile, flexural, and unnotched impact tests per ISO standards, revealed that the modified systems exhibited tensile strengths of 63.4 MPa (MeSZ-1) and 71.2 MPa (MeSZ-2), flexural strengths of 119.9 MPa and 127.1 MPa, and impact strengths of 39.1 kJ/m2 and 30.9 kJ/m2, respectively—comparable to or surpassing controls while balancing toughness and rigidity. Thermal properties were assessed via differential scanning calorimetry (DSC) for glass transition temperature (Tg: 122.3 °C for MeSZ-1, 175.5 °C for MeSZ-2), thermogravimetric analysis (TGA) showing elevated 5% weight loss temperatures (386.3 °C and 401.8 °C) and char yields (10.8% and 13.8%), isothermal weight loss at 400 °C with >80% retention after 120 min, and Tg attenuation during 200 °C aging (78.7% and 83.8% retention after 1000 h). The enhanced thermal stability is attributed to Si-O/Si-N bonds forming protective inorganic barriers against oxidation. Overall, these silazane-modified curing agents offer promising advancements for high-temperature epoxy applications, combining mechanical robustness with superior thermal endurance.