Microwave assisted synthesis and determination of chain branching in solid epoxy resins using 1H NMR spectrometry

The degree of branching in solid epoxy resins (epoxy value EV = 0.11 mol/100 g) prepared under microwave and conventional conditions has been investigated by H-1 NMR spectrometry. The applied method involves rapid reaction between trichloroacetyl isocyanate and hydroxyl groups incorporated in the epoxy resin structure. Solid epoxy resins were prepared by polyaddition of Bisphenol A (BPA) to a lower-molecular-weight (L-M) epoxy resin (Rutapox 0162, EV = 0.57) in the presence of 2-methylimidazole (2-MI) as a catalyst. All the microwave reactions were performed in the multimode microwave reactor Plazmatronika-Poland with microwave frequency of 2.45 GHz and maximum of microwave power of 600 W. The results show that the degree of branching in resins synthesized under microwave irradiation is comparable with those obtained under conventional heating (i.e. 6-12%) and is not influenced by the reduction of reaction time. (C) 2003 Elsevier Ltd. All rights reserved.