Novel organic–inorganic hybrid materials based on epoxy-functionalized silanes

Hybrid materials comprising inorganic glasses and organic polymers were investigated as potential replacements for diglycidyl ether of bisphenol-A to improve the thermomechanical properties of available composites. An epoxy-functionalized silane, 3-glycidoxypropyltrimethoxysilane (GPTMS), was employed to synthesize organic–inorganic hybrid materials (OIHMs) via a sol–gel process. The oxirane ring in GPTMS was cross-linked by compounds including an aliphatic amine, diethylenetriamine, amine-functionalized silane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, tertiary amine, 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and an acid anhydride, hexahydrophthalic anhydride. OIHMs derived from a difunctional organosilane, (3-glycidoxypropyl)methyldimethoxysilane, were also synthesized to compare the mechanical properties with OIHMs derived from GPTMS. Structural characterization of cured OIHMs was performed using a combination of attenuated total reflectance spectroscopy (FTIR-ATR) and 29Si solid-state nuclear magnetic resonance. Differential scanning calorimetry and thermogravimetric analysis were used to clarify the thermal properties. The thermomechanical properties and cross-link density were evaluated using dynamic mechanical thermal analysis (DMTA). In this study, it was evident that the presence of inorganic networks provided a significant improvement of the thermomechanical properties, where the glass transition temperature typically increases by 20 °C and the storage modulus at 150 °C by nearly eight times that of neat epoxy resin. An increase in glass transition temperature, end-use temperature, and the thermomechanical behavior of OIHMs was observed and quantified using DMTA. These results corresponded to calculated increases in cross-link density.