Polyhexahydrotriazines (PHTs) are polymers of

hexahydro-1,3,5-triazine In chemistry, hexahydro-1,3,5-triazine is a class of heterocyclic compounds with the formula (CH2NR)3. They are reduced derivatives of 1,3,5-triazine, which have the formula (CHN)3, a family of aromatic heterocycles. They are often called triaza ...

s, a class of heterocyclic compounds with the formula (CH₂NR)₃. They are among the strongest known

thermosetting plastics In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by Reversible process (thermodynamics), irreversibly hardening ("curing (chemistry), curing") a soft solid or viscous liquid prepolymer (resin) ...

and are stable to solvents at pH > 3, but decompose to the

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 ...

s in acidic solutions.

Synthesis

Various PHTs have been synthesized at room temperature in one step in the early 2000s; they were considered impractical due to their poor mechanical properties. It was later elucidated that, due to the temperature of synthesis, the poor mechanical properties observed were likely due to poly(hemiaminal) formation and not PHT formation. In 2014, Jeanette Garcia, Gavin Jones and a team of researchers at

IBM Almaden Research Center IBM Research is the research and development division for IBM, an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. IBM Research is the largest industrial research or ...

, US, developed a new type of PHT (1.6) in what has been called a "happy accident". Garcia had left out a reagent when preparing her mix of chemicals. When low heat was applied to the beaker of

paraformaldehyde Paraformaldehyde (PFA) is the smallest polyoxymethylene, the polymerization product of formaldehyde with a typical degree of polymerization of 8–100 units. Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition. Paraf ...

and 4,4ʹ-oxydianiline, it had created a hemiaminal dynamic covalent network (HDCN). Heating the HDCN to 200 °C transformed it into two new polymers: PHT 1.6 and an organogel known as polyhemiaminal (PHA)

Properties

The PHT 1.6 has a yellowish color. It is resistant to solvents at pH > 3, but decomposes into monomers within a day in acidic solutions at pH < 2. This property is unusual for thermosetting plastics and allows easy recycling. This PHT has a

Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied le ...

exceeding 10 GPa, which is among the highest for a

thermosetting plastic 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 ...

; it can be further increased by ~50% by dispersing carbon nanotubes in the polymer. The PHT is brittle, and cracks when strained to 1%. Upon heating, it softens at a glass transition temperature of ~190 °C and decomposes at ~300 °C.

Possible uses

A number of industries could benefit from the use of PHT in

manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to ...

parts and devices due to its

recyclability Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

, lightweight structure, and strength: *

Aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astr ...

- PHT used in the development of wings, tails, bodies, and rutters would provide a lightweight, durable vessel for both commercial and personal

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...

applications. PHT in combination with PHA could be used to adhere aircraft pieces that are exposed to harsh environmental conditions and high speeds. * Automotive - When manufacturing automobiles, PHT would provide a light, high performance option for auto body parts such as panels, hoods, and exterior trim pieces. *

Semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

s - Semiconductor chips and

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

s made of PHT would allow for the reworking of defective electronics rather than having to discard the equipment.

References

{{reflist Amines Triazines Organic polymers Thermosetting plastics