Isophthalic Acid

Isophthalic acid (PIA) is a non-toxic organic compound with the formula C6H4(CO2H)2. This colorless solid is an isomer of phthalic acid and terephthalic acid. These aromatic dicarboxylic acids are used as precursors (in the form of acylchlorides) to commercially important polymers. The high-performance polymer polybenzimidazole is produced from isophthalic acid.


Isophthalic acid (PIA) has three major uses:

  • PET (PolyEthylene Terephthalate) copolymer, which is used in bottle resins and to a much lesser extent, for fibers. PIA (Purified Isophthalic Acid) reduces the crystallinity of PET, which serves to improve clarity and increase the productivity of bottle-making.
  • Unsaturated polyester resins, where the addition of PIA improves thermal resistance and mechanical performance, as well as resistance to chemicals and water.
  • Polyester/alkyd surface coating resins, where PIA increases resistance to water, overall durability and weatherability.

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Isophthalic acid is a colorless crystalline solid. It is used as an intermediate primarily for unsaturated polyester resins and alkyd and polyester coating resins; other applications include use in aramid fibers, as a component of copolyester resins and in high-temperature polymers. Nearly pure isophthalic acid has a purity of >99.8%. This material is called purified isophthalic acid or PIA.

IPA has excellent performance characteristics including exceptional hardness, corrosion and stain resistance, hydrolytic stability of coatings and gel coats, outstanding thermal stability and low resin color in coatings industry.

Isophthalic acid is a key ingredient in FRP (Fiberglass Reinforced Plastics) markets for such products as marine, automotive, and corrosion resistant pipes and tanks. Polyesters containing isophthalic acid are also used extensively in industrial coatings applications for home appliances, automobiles, aluminum siding, and metal office furniture. It used as an intermediate for polyesters, polyurethane resins, plasticizers.

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