Chemistry of novolac resins. X. Polymerization studies of HMTA and strategically synthesized model compounds

Abstract

The reactions between hexamethylenetetramine (HMTA) and compounds which model novolac resins have been studied by 13C- and 15N-NMR techniques. The dimer and tetramer compounds vary in molecular size and structure and react with HMTA to yield benzylamines and benzoxazine as the major initial-formed intermediates and convert to methylene linked compounds at increased temperatures. The reaction of the compounds with only ortho reactive sites paralleled the 2,4-xylenol–HMTA case reported by us previously; however, increasing molecular weight favored the formation of benzylamines and not benzoxazines. Those compounds with only para reactive sites paralleled the 2,6-xylenol–HMTA case. The reactivity of the systems containing both ortho and para reactive sites depends on the ratio of ortho/para sites and various aspects such as the chemical structure and molecular weight of the compound, the HMTA level, and the melting point and pH of the system. These results parallel those obtained from novolac/HMTA systems. The xylenol/HMTA reactions formed similar products but showed quite different relative reaction rates by varying the HMTA ratio and structures of the materials. The importance of careful selection of model systems is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1347–1355, 1999