Polybenzoxazines, also called benzoxazine resins, are cured polymerization products derived from
benzoxazine monomer
A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization.
Classification
Chemis ...
s.
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 ring, fused with a benzene ring. The systematic
IUPAC name 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 organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
, a
phenol
Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire.
The molecule consists of a phenyl group () ...
and
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...
, 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) 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 Solubility, soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on a ...
, bisphenol-F, thiodiphenol or dicyclopentadienediphenol.
Synthesis
Benzoxazines can be prepared by a one-pot process by heating an
aromatic amine
In organic chemistry, an aromatic amine is an organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be a ...
, 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 Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...
and
phenolic resin
Phenol formaldehyde resins (PF), also called phenolic resins or 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 commercial synthetic ...
s 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
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 advantage ...
. They are substitutes of
epoxy
Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...
,
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 board
A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...
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
The glass–liquid transition, or glass transition, is the gradual and Reversible reaction, reversible transition in amorphous solid, amorphous materials (or in amorphous regions within Crystallinity, semicrystalline materials) from a hard and rel ...
temperature and degradation were improved by the copolymerization.
Advantages
* No
volatile release during cure
*
Viscosities
Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for example, syrup h ...
as low as 1000
cP at processing temperatures
* Near zero shrinkage
*
Room temperature
Room temperature, colloquially, denotes the range of air temperatures most people find comfortable indoors while dressed in typical clothing. Comfortable temperatures can be extended beyond this range depending on humidity, air circulation, and ...
storage stability
* Gel times of as short as 17 minutes at 155 °C
* Good
hydrophobicity
In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly intermolecular force, repelled from a mass of water. In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to b ...
* 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 insul ...
and
dissipation
In thermodynamics, dissipation is the result of an irreversible process that affects a thermodynamic system. In a dissipative process, energy ( internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, wh ...
factors)
* Good chemical resistance
See also
*
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 ...
*
Thermoset polymer matrix
*
Plastic
Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
References
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Benzoxazines
Adhesives
Organic polymers
Synthetic resins
Thermosetting plastics