CURING OF EPOXY OLIGOMERS BY ISOCYANATES

The curing of epoxy oligomers by isocyanates, as a function of structure and ratio of components, as well as of synthesizing conditions, has been studied. It was found that differences exist in reactions occurring during epoxy-isocyanate formation in bulk and in thin layer on substrate. The aspects studied were the effect of the structure of epoxy oligomers and isocyanates on relative reactivity of oligomers and on polymer formation and their structural changes depending on synthesizing temperature. Epoxy oligomers and isocyanates of various chemical structures were investigated by i.r. spectrography, differential thermal analysis, chemical analysis, electrical relaxation and electron microscopy. It is shown that the interaction between epoxy oligomers and isocyanates comprises two consecutive stages: formation of urethanes and 2-oxazolidones. The presence of tertiary nitrogen atoms in the structure of epoxy oligomer or isocyanate causes additional trimerization of isocyanate and formation of isocyanurate cycles. The structure of epoxy oligomer and isocyanate essentially influences their relative reactivity in the formation of oxazolidones and determines the temperature ranges in which these reactions take place. It is also shown that the conditions of formation and the ratio of components have a considerable effect on the chemistry of interaction in the epoxy-isocyanate oligomeric system. The interaction temperature in the epoxy-isocyanate system is the cause of varied degree of cross-linking, topological and supermolecular structure of polymers.