Benzoxazine is a type of bicyclicheterocyclicchemical compound that contains oxygen and nitrogen in an unsaturated six-member ring, fused with a benzene ring. It can refer to the monomer, as well as the cured polymerization product of those monomers, also called benzoxazine resins or polybenzoxazines.
Benzoxazine monomer
Benzoxazines are bicyclic heterocyclic compounds containing one oxygen and one nitrogen atom in a doubly unsaturated six-member ring, specifically a 1,3-oxazine ring, fused with a benzene ring. The systematic benzoxazines IUPAC name of the unsubstituted monomer is 3,4-dihydro-3-phenyl-2H-1,3-benzoxazines. Benzoxazines are products of condensation between an amine, a phenol and formaldehyde, used to producethermoset resins or thermosetting polymer. Because of the wide availability and low-cost of starting materials, as well as ease of preparation diverse benzoxazines are available. Numerous research focus on the different curing temperature, and polymer properties, such as cross-linking, from benzoxazines derived from substituted phenols. Commercial benzoxazines by Huntsman are based on bisphenols: bisphenol-A, bisphenol-F, thiodiphenol or dicyclopentadienediphenol.
Synthesis
Benzoxazines can be prepared by a one-pot process by heating an aromatic amine, a phenol and formaldehyde. Alternatively, they can be prepared sequentially.
Curing
Curing of benzoxazines takes place by thermal ring-opening polymerisation with or without catalyst. Benzoxazines can be homopolymerized to yield rigid materials, or can be copolymerized with other monomers to tune properties.
Polybenzoxazine
The result of heating up benzoxazine monomer is a high molecular weightthermoset polymer matrix. Composites of it are used where enhanced mechanical performance, flame and fire resistance compared to epoxy and phenolic resins is required. Polybenzoxazines are a class of halogen-free high-performance polymers. The main applications of polybenzoxazines resins are in fibre-reinforced plastic and as adhesives. They are substitutes of epoxy, phenolic and bismaleimide resins. Because of their superior resistance to chemicals, low flammability, and excellent heat stability, they are used for components that are exposed to high temperatures and corrosive media. Examples include chemical and heat resistant coatings, adhesives, prepregs, and encapsulants as well as halogen-free laminates for printed circuit boards. Polybenzoxazines are also used in the automotive and aerospace industries for applications where superior thermal and mechanical properties relative to conventional resins are required.
