NMR INVESTIGATIONS OF THE POSSIBLE CROSS-REACTIONS BETWEEN CYANATE AND EPOXY-RESINS

The possible cross reactions indicated by solid-state NMR between cyan ate functionalized resin and epoxy functionalized resin have been inve stigated by using both natural abundance and labeled monofunctional mo del compounds. These soluble products were isolated and purified by si lica gel adsorption chromatography and gel permeation chromatography. They were fully characterized by high resolution H--1, C--13, N-15-NMR spectroscopy and by mass spectrometry. The major cross-reaction produ ct is a racemic mixture of enantiomers, which contain an oxazolidinone ring formed by one cyanate molecule and two epoxy molecules. However, epoxy consumption lags cyanate consumption in the overall reaction as triazine formation from the cyanate is much faster than the two compe ting reactions, the cross reaction between cyanate and epoxy, and the self-polymerization of epoxy, under the conditions investigated. The c ross reaction between cyanate and epoxy is limited. Approximately 12% of cross reaction between cyanate and epoxy was found in the overall r eaction. In addition to the cross reactions of epoxy and cyanate, the reactions of epoxy and the carbamate, which is the major side product for the curing reaction of cyanate resin in solution, have also been i nvestigated, and the mechanism of these reactions discussed. From the reactions of epoxy and carbamate, several products related to cross re action between epoxy and cyanate have been isolated and identified. It is suggested that the reaction of epoxy and carbamate is one of the p athways in the overall cross reaction between epoxy and cyanate resins . Finally, the mechanism of the overall cross-curing reaction between the diepoxy and dicyanate mixed resins is discussed. (C) 1994 John Wil ey & Sons, Inc.