The chemistry of novolac resins - V. Reactions of benzoxazine intermediates

Abstract

As part of our study on the curing reactions between novolac resins and hexamethylenetetramine (HMTA), a model benzoxazine, 3-(3,5-dimethyl-2-hydroxybenzyl)-6,8-dimethyl-3,4-dihydro-(2H)-1,3-benzoxazine, was heated under carefully controlled conditions, and the structural changes were studied by 13C and 15N n.m.r. spectroscopy. The benzoxazine structure is relatively stable, and detectable decomposition only occurred about 185°C with the formation of methylene linkages between phenolic rings. Various nitrogen-containing structures, such as amides, amines and imines, together with hydroxybenzyl alcohol, bis(ortho-hydroxybenzyl) ether, hydroxybenzaldehyde and ortho-hydroxybenzoic acid, are als..