Polybenzoxazines, also called benzoxazine resins, are cured polymerization products derived from

benzoxazine Benzoxazines are a group of isomeric bicyclic heterocyclic chemical compounds that consist of a benzene ring fused to an oxazine ring. The different isomers depend on the relative positions of the oxygen and nitrogen atoms in the oxazine ring, on ...

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

Monomers

Benzoxazines are bicyclic heterocyclic compounds containing one oxygen and one nitrogen atom in a doubly unsaturated six-member ring, specifically a 1,3-

oxazine Oxazines are heterocyclic compounds containing one oxygen and one nitrogen atom in a doubly unsaturated six-membered ring. Isomers exist depending on the relative position of the heteroatoms and relative position of the double bonds. By extensi ...

ring, fused with a benzene ring. The systematic

IUPAC name In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among the possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for cho ...

of the prototypical unsubstituted monomer is 3,4-dihydro-3-phenyl-2''H''-1,3-benzoxazine. Benzoxazines are products of condensation between an

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

, a

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

and

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

, used to produce

thermoset In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...

resins or

thermosetting polymer In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...

. Because of the wide availability and low-cost of starting materials (amines, phenols and formaldehyde), as well as ease of preparation (

one-pot reaction In chemistry a one-pot synthesis is a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor. This is much desired by chemists because avoiding a lengthy sepa ...

) 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 A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on an industrial s ...

, 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. (Catalysts reduce curing temperature.) Benzoxazines can be homopolymerized to yield rigid materials, or can be copolymerized with other monomers to tune properties.

Polymers

The result of heating up benzoxazine monomers is a high molecular weight thermoset polymer matrix. Composites of it are used where enhanced mechanical performance, flame and fire resistance compared to

epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

and

phenolic resin Phenol formaldehyde resins (PF) or phenolic resins (also infrequently called phenoplasts) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commerc ...

s is required. Polybenzoxazines are a class of halogen-free high-performance polymers. The main applications of polybenzoxazines resins are in

fibre-reinforced plastic Fibre-reinforced plastic (FRP; also called fibre-reinforced polymer, or in American English ''fiber'') is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fib ...

and as

adhesives Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

. They are substitutes of

phenolic Phenolic is an adjective and a substantive (noun) that may apply to : * Phenol (or carbolic acid), a colorless crystalline solid and aromatic compound * Phenols, a class of chemical compounds that include phenol * Phenolic content in wine * Phenol ...

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,

prepreg Pre-preg is a composite material made from "pre-impregnated" fibers and a ''partially cured'' polymer matrix, such as epoxy or phenolic resin, or even thermoplastic mixed with liquid rubbers or resins. The fibers often take the form of a weave ...

s, and encapsulants as well as halogen-free laminates for

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

s. Polybenzoxazines are also used in the automotive and aerospace industries for applications where superior thermal and mechanical properties relative to conventional resins are required.

Copolymers

It has been reported that it is possible to copolymerize benzoxazines with other monomers such as epoxy and urethane. This copolymerization could lead to higher crosslink network density and, consequently, to improvement in properties. In fact, experimental data reveals improvement in thermal properties. Glass transition temperature and degradation were improved by the copolymerization.

Advantages

* No volatile release during cure *

Viscosities The viscosity of a fluid is a measure of its drag (physics), resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quant ...

as low as 1000 cP at processing temperatures * Near zero shrinkage * Room temperature storage stability * Gel times of as short as 17 minutes at 155 °C * Good

hydrophobicity In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

* Gel temperature T_g at 140 - 250 °C or higher * Excellent electrical properties (low

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

and

dissipation In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a ...

factors) * Good chemical resistance

References

{{Reflist Benzoxazines Adhesives Organic polymers Synthetic resins Thermosetting plastics