Synthesis and characterization of epoxy resins prepared under microwave irradiation

A new microwave‐assisted method of synthesis of solid epoxy resins (SER) with desired epoxy‐groups content is described. The method is based on the polyaddition of 4,4′‐isopropylidenediphenol (BPA) to a lower‐molecular‐weight epoxy resin [Rütapox 0162, epoxy value (EV) = 0.57 mol/100 g] in the presence of 2‐methylimidazole (2‐MI), as a catalyst. Analogical syntheses were performed using conventional heating (i.e., electric heating mantle) for the comparison of properties of SER under both conditions. All the microwave reactions were carried out in the multimode microwave reactor Plazmatronika (Poland) with microwave frequency of 2.45 GHz and maximum microwave power of 600 W. The main advantage of the microwave process is twofold reduction of reaction time in comparison to the conventional heating. Values of EV, Mn, Mw, Mw/Mn, and degree of branching of the products obtained were determined. It was found that the molecular weight distribution and degree of branching in resins synthesized under microwave irradiation was comparable with those obtained under conventional heating and was not influenced by the reduction in reaction time.