3.2. Synthesis of Hybrid Oligomer Based on the Epoxy Methacrylate Resin

The synthesis of epoxy methacrylate (EA) resin was carried out in a 250 mL three-neck glass reactor (equipped with a thermometer, a condenser, a nitrogen inlet, and a mechanical stirrer), into which bisphenol A type epoxy resin and hydroquinone as a radical scavenger (0.0075 wt% based on total batch weight) was added into the reactor at room temperature. Then, methacrylic acid (0.5 mol relative to resin epoxy value) and catalyst–triphenylphosphine in the amount of 0.8 wt% (relative to the mass of MAA) were added. The mixture was heated to 70 °C using an oil bath and stirred (120 RPM) to obtain the homogenous mixture. The final reaction temperature was set to 90 °C, and the process was conducted for 5 h in a nitrogen atmosphere, with stirring. The above synthesis parameters were established based on a literature survey [10,20,21,22,23] and our own experience [19,36]. The reaction products appear as colorless, transparent, viscous liquids. The general reaction scheme for the addition of methacrylic acid to epoxy resin, together with the expected products, is presented in Figure 9.

Synthesis of epoxy methacrylate resin.