Preparation and characterization of epoxy resin modified with alkoxysilane- functionalized poly(urethane-imide) by the sol-gel process

The sol-gel process has been frequently employed for preparation of high performance silica/polymer composites. In this paper, novel sol-gel precursor triethoxysilane-terminated poly(urethane-imide) (PUI-Si), combining the advantages of polyurethane (PU) and polyimide, was synthesized and characterized. Then PUI-Si was incorporated into the epoxy resin matrix to prepare a series of EP/PUI-Si organic-inorganic hybrids through an in situ sol-gel process and crosslinking reactions. The thermal stability of EP/PUI-Si hybrids was evaluated by thermogravimetric analysis and the results show that the PUI-Si could significantly improve the thermal properties of epoxy resin. The initial decomposition temperature of composites with 50 wt% PUI-Si reached 347.1 °C, 157.3 °C higher than that of neat epoxy resin. Furthermore, the tensile strength and breaking elongation can also be clearly improved by adding a suitable amount of PUI-Si. Similarly, the water contact angle increased to 97.4° with 70 wt% PUI-Si, showing a hydrophobic surface. The morphology was investigated by transmission electron microscopy and the results reveal that the silica particles are smaller than 20 nm and have a strong interaction with the epoxy resin matrix, resulting in the above-mentioned high performance properties.