Compounds with bifunctional benzoxazine groups in their molecular structures form crosslinked structures characteristic of phenolic materials through a ring‐opening reaction mechanism. This family of compounds offers greater flexibility than conventional novolac or resole resins in terms of molecular design. It is also superior to conventional phenolic resin in process control since it releases no by‐product during curing reactions. The materials thus obtained exhibit excellent mechanical integrity with glass transition temperatures over 200°C. The synthesis, composition, and structural analysis of precursors based on bisphenol‐A are discussed herein. © 1994 John Wiley & Sons, Inc.

A new class of phenolic‐like thermosetting resins has been developed that is based on the ring‐opening polymerization of a benzoxazine precursor. These new materials were developed to combine the thermal properties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems. The polybenzoxazines overcome many of the traditional shortcomings of conventional novolak and resoletype phenolic resins, while retaining their benefits. The physical and mechanical properties of these new polybenzoxazines are investigated and are shown to compare very favorably with those of conventional phenolic and epoxy resins. The ring‐opening polymerization of these new materials occurs with either near‐zero shrinkage or even a slight expansion upon cure. Dynamic mechanical analysis reveals that these candidates for composite applications possess high moduli and glass transition temperatures, but low crosslink densities. Long‐term immersion studies indicate that these materials have a low rate of water absorption and low saturation content. Impact, tensile, and flexural properties are also studied. Results of the dielectric analysis on these polybenzoxazines demonstrate the suitability of these materials for electrical applications. © 1996 John Wiley & Sons, Inc.

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Benzoxazine-based phenolic resin has recently attracted a great deal of attention due to its versatile properties. This paper explores yet another interesting property shown by this class of phenolic resin:  volumetric expansion upon polymerization. It is proposed that the volumetric expansion of the benzoxazine resin is mostly due to the consequence of molecular packing influenced by inter- and intramolecular hydrogen bonding. The role of hydrogen bonding on the volumetric expansion has been studied by systematically changing the primary amine used in the benzoxazine monomer synthesis. In comparison to the other known expanding monomer, spiroortho compounds, this resin has been shown to have a high potential for structural/engineering applications. The homopolymers of this resin have a high glass transition temperature (T g).

A series of benzoxazine compounds have been prepared from different bifunctional phenols and primary amines and the molecular compositions of the precursors are characterized by nuclear magnetic resonance, Fourier transform infrared, and size exclusion chromatography. It has been demonstrated that by design of the molecular structures of the benzoxazine precursors, therefore by tailoring of the network molecular architectures, new phenolic materials with superior mechanical and thermal properties, and ease‐of‐processing characteristics can be obtained. The characteristics of dynamic mechanical spectra of the phenolic materials are studied and related to their structural features. © 1994 John Wiley & Sons, Inc.