Chapter 12 - Hydrogen Bonding of Polybenzoxazines

Abstract

The hydrogen-bonded structure of polybenzoxazine is simply explained by the fact that the strength of hydrogen bonding is dependent on the electronegativity of the side group that is attached to the nitrogen atom. Polybenzoxazines, a novel class of polymers that offer many unusual and excellent properties, are recently developed and characterized by Ishida. As a wide variety of benzoxazine monomers can be easily obtained by changing the phenolic and/or primary amine component in Mannich condensation, they are of great interest for commercial applications. Furthermore, these resins have many excellent properties, which easily surpass those of many other thermosetting resins, such as excellent mechanical properties, high char yield, near zero volumetric shrinkage/expansion on polymerization, low water absorption, excellent resistance to chemicals, and UV light, as well as amazingly high transition temperature (Tg), even with rather low cross-link density. A possible explanation for these unusual properties is the formation of extensive hydrogen-bonding networks. This chapter reviews the recent progress in the investigation of the hydrogen-bonded network structure of polybenzoxazines using well-designed polybenzoxazine model dimers, oligomers, and polybenzoxazines. Additionally, the generalized explanation between the physical properties of polybenzoxazines and the hydrogen-bonded network structure are explained in this chapter. Generalized explanations for the relationships between the hydrogen-bonded network structure and the excellent properties of polybenzoxazines, such as volumetric expansion, water absorption, and resistance to carboxylic acids are also discussed. Further, influence of the unique hydrogen-bonding schemes on the application of polybenzoxazine and its blends is also discussed in detail by investigating the 2D correlation spectroscopy, surface free energy, and FT-IR of the various blends.