STUDY OF THE CURING REACTION OF EPOXY-RES IN BY NEAR-INFRARED LASER-EXCITED FT-RAMAN SPECTROMETRY

In the present investigation we examined the curing reaction of epoxy resin using acid anhydride as a curing agent by near-infrared laser-ex cited FT-Raman spectrometry. The sample system was as follows. Diglyci dyl-ether-bisphenol A (DGEBA) was used as the main agent, methyl nadic anhydride (MNA) as the curing agent, and 2-ethyl-4-methylimidazole (E MI) as the curing catalyst. Though this sample system is widely used i n practice, quantitative or semi-quantitative examinations of the curi ng reaction have not yet been sufficiently developed. This situation i s assumed to result from the fact that in infrared spectrometry the ch aracteristic bands of the main agent severely overlap with those of th e curing agent. On the other hand, in the usual Raman spectrometry usi ng laser light in the visible region, a very strong fluorescent backgr ound is generated from this sample system illuminated by laser beam, a nd the spectra are hidden in this background. It was shown that when F T-Raman spectrometry is performed with a near-infrared laser as an exc itation source very clear spectra consisting of sharp bands can be obt ained, and the characteristic signals of each of the chemical species involved in the curing reaction in question can be recognized. On the basis of these characteristic Raman signals, the effect of the quantit ies of the curing catalyst on the curing phenomena was examined. It wa s proven that when the quantity of EMI is in the concentration range f rom 0.2 wt% to 2 wt%, EMI promotes a polymerization reaction between t he main agent DGEBA and the curing agent MNA, which is the situation t hat we had expected to realize. On the other hand, when the concentrat ions of EMI are larger than 2 wt%, it is clear that the reaction schem e changes, and that the reaction between DGEBA and EMI takes priority over the desired curing reaction. It was concluded that the thus-obtai ned information is very important for the optimum curing characteristi cs of epoxy resin.