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ABSTRACT
A concise meticulous study on acrylation of diglycidylether bisphenol A (DGEBA) epoxy resin was carried out through the reaction with acrylic acid in the presence of triphenyl-phosphine under conventional heating, ultrasonic waves, as well as microwave irradiation. The conversion of epoxy to ester group was monitored by FTIR spectroscopy and epoxy equivalent value (EEV) measurements. The main advantage of the microwave and ultrasound processes was significant reduction of reaction time in comparison with the conventional heating. Thus, the reaction time was reduced from hours (for conventional heating) to minutes (for ultrasonic method) and even to seconds (for microwave method). The final epoxy-acrylate vinyl ester resin products were characterized by FTIR spectroscopy and epoxy equivalent values. Since the products may be industrially formulated as light curable resins, and they are widely used in allied industries. Therefore, this highly accelerated production of the resins can be considered as an important economical issue.
KEY WORDS: Epoxy-acrylate resin, Vinyl ester, Microwave irradiation, Ultrasound, Synthesis.
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1. INTRODUCTION
Epoxy resins, oligomers with oxirane functionality, have been widely used in many industrial applications because of their superior properties particularly versatility, so that they are probably the most versatile contemporary plastics[1]. The presence of double bonds unsaturation produced from the reaction with acrylic monomers modifies epoxy resins, as epoxy-acrylate or (vinyl ester) resins, for being used in the radiation curing industry[2] and for vinyl ester based polymer composites.
Epoxy acrylates are widely used in UV-curable coatings because of their low costs; fast curing rate; and high gloss, hardness, and chemical resistance of the cured films[3]. They have found variety of applications in coatings, electronics, paints, inks, adhesives, etc.[4,5]. One of the most important ways to synthesize these oligomers is reaction of epoxy resin with ethylenically unsaturated carboxylic acids (e.g., acrylic or methacrylic acid) in the presence of an esterification catalyst[6,7]. In general, any esterification catalyst is suitable for use to prepare vinyl ester including the tertiary phosphines or amines, metal hydroxides, tin salts, ammonium, phosphonium or sulfonium salts, and imidazole derivatives[6]. The reaction is usually carried out for a couple of hours at the temperature range 70-120 °C with air or N2 blanket to inhibit vinyl polymerization[6,8,9].
In the past few decades, it was shown...