Studies on polyimides: Part 3. Interactions between hexamethylenetetramineand models for polyimides and novolacs

The interactions between hexamethylenetetramine (HMTA) and models for both poly(N-(hydroxyphenyI) maleimides) and phenol-formaldehyde resins have been examined. There is direct interaction between HMTA and the N-(hydroxypheny I) succinimide and xylenols used as model compounds. When the model compoun ds both contain a free ortho position, four different benzoxazine derivativ es are formed, that is, the succinimide-succinimide and xylenol-xylenol ben zoxazines and the two 'mixed' systems. The rate of reaction of HMTA with th e mixed system was measured via C-13 nuclear magnetic resonance spectroscop y (n.m.r.). The relative rates of formation of the benzoxazine derivatives are dependent on the substitution pattern of the phenolic rings. Control ov er the interactions between HMTA and the models was achieved via selective masking of the phenolic groups using the thermally labile tetrahydropyranyl (THP) group. (C) 1999 Elsevier Science Ltd. All rights reserved.