Pyromellitic dianhydride (PMDA) 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 any chemical compound that contains carbon. For example, carbon-co ...

with the formula C₆H₂(C₂O₃)₂. It is the double carboxylic acid anhydride that is used in the preparation of

polyimide Polyimide (sometimes abbreviated PI) is a monomer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, suc ...

polymers such as

Kapton file:Kaptonpads.jpg, Kapton insulating pads for mounting electronic parts on a heat sink Kapton is a polyimide film used in flexible printed circuits (flexible electronics) and space blankets, which are used on spacecraft, satellites, and variou ...

. It is a white, hygroscopic solid. It forms a hydrate.

Preparation

It is prepared by gas-phase

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of 1,2,4,5-tetramethylbenzene (or related tetrasubstituted benzene derivatives). An idealized equation is: :C₆H₂(CH₃)₄ + 6 O₂ → C₆H₂(C₂O₃)₂ + 6 H₂O In the laboratory, it can be prepared by dehydration of pyromellitic acid using

acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of c ...

Reactions

PMDA is an electron-acceptor, forming a variety of

charge-transfer complex In chemistry, charge-transfer (CT) complex, or electron donor-acceptor complex, describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic force ...

es. It reacts with amines to diimides, C₆H₂ CO)₂NRsub>2 which also have acceptor properties.

Applications

PMDA is used in

PET bottle recycling Polyethylene Terephthalate (Polyethylene terephthalate, PET) is one of the most common polymers in its polyester family. Its global market size was estimated to be worth 37.25 billion USD in 2021. Polyethylene terephthalate is used in several a ...

as a chain extender. It increases the molecular weight of the polymer by linking-together alcohol and carboxylic acid groups formed by hydrolysis of the PET. This improves the rheological properties and overall quality of the recycled plastic.

Safety

Evidence suggests that PMDA causes

occupational asthma Occupational asthma is new onset asthma or the recurrence of previously quiescent asthma directly caused by exposure to an agent at workplace. It is an occupational lung disease and a type of work-related asthma. Agents that can induce occupationa ...

References

{{Reflist Phthalic anhydrides