Organic–inorganic hybrid coatings prepared from glycidyl carbamate resin, 3-aminopropyl trimethoxy silane and tetraethoxyorthosilicate

Hybrid sol–gel coatings were formulated from glycidyl carbamate (GC) resins, 3-aminopropyltrimethoxy silane (APTMS) and tetraethoxyorthosilicate (TEOS) as the inorganic network former. GC and silane-modified GC resins were synthesized and then characterized using Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance Spectrometry (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The resins were crosslinked with amine crosslinkers such as p-aminocyclohexyl methane (PACM), Ancamide 2050, Ancamide 2353 and Epikure 3164 at 1:1 equivalent ratio of the epoxy groups in the synthesized resin and amine crosslinker. The TEOS content in the coatings were varied to understand its effect on the coating properties. The hybrid coatings were cured at room temperature and humidity for more than 20 days as well as oven cured at 80 °C for 1 h. The thermal properties of the post-cured hybrid materials were evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical property evaluation such as König pendulum hardness measurement, impact resistance and crosshatch adhesion tests of the post-cured samples were carried out. MEK double rub resistance and water contact angle of the coatings were also evaluated. All of the coatings had good adhesion to aluminum 2024-T3 and had good MEK double rub resistance, indicating good crosslinking. Properties such as Tg, hardness and flexibility varied with the amine crosslinker used with Epikure 3164 yielding the lowest Tg, highest flexibility, and lower hardness coatings. Increasing the amount of TEOS modification in the formulations increased the hardness, the Tg, and the thermal stability. The flexibility – determined using reverse impact measurements – also increased with increasing TEOS content.