ISOPHTHALIC ACID- ▸ Unsaturated polyesters: Diacid for high-performance UPR and gel coats.
- ▸ PET/specialty resins: Comonomer with terephthalic acid in bottle and specialty resins.
- ▸ Alkyd and coating resins: Building block for coating polyesters and alkyds.
- ▸ Wire enamels: Used in wire enamel formulations.
- ▸ Adhesives and inks: Component in adhesive and ink resins.
A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
Request SDS →Isophthalic acid (CAS 121-91-5) is an aromatic dicarboxylic acid used to build high-performance polyesters and alkyd resins. Industry references record its use as a comonomer with terephthalic acid in bottle and specialty resins, in high-performance unsaturated polyesters, and in adhesives, inks, and wire enamels. Supplied as a bulk acid intermediate.
Regulatory & registration requirements
- TSCA (US):
- REACH (EU):
- EC number: 204-506-4
Source: EPA TSCA Inventory (July 2025 release) · ECHA CHEM — retrieved 2026-07-12
Frequently Asked Questions
What is isophthalic acid used for?
Isophthalic acid (IPA, CAS 121-91-5) is an aromatic dicarboxylic acid used to build high-performance polyesters and alkyd resins. It serves as a diacid for high-performance unsaturated polyesters and gel coats, as a comonomer with terephthalic acid in bottle and specialty resins, and in coating polyesters, wire enamels, adhesives, and inks.
What is the difference between isophthalic acid and terephthalic acid?
Both are aromatic dicarboxylic acids (C8H6O4) but differ in ring substitution: isophthalic acid has its two carboxyl groups in the meta (1,3) position, terephthalic in the para (1,4) position. The meta geometry of isophthalic acid gives resins improved toughness and chemical/corrosion resistance, and it is often used as a comonomer with terephthalic acid.
What is isophthalic resin used for?
Isophthalic (iso) unsaturated polyester resins are used where higher mechanical performance and chemical/corrosion resistance are needed, such as gel coats, marine and corrosion-resistant laminates, and specialty composites. Isophthalic acid is the diacid building block for these high-performance UPR systems.
What is the CAS number and HS code for isophthalic acid?
The CAS number is 121-91-5, the molecular formula is C8H6O4, and the HS classification is 2917.39 (aromatic polycarboxylic acids and their anhydrides, other). Lot-specific identity and specification are confirmed on the Certificate of Analysis.
How is isophthalic acid supplied in bulk and what is the cost?
We supply isophthalic acid as a bulk acid intermediate in industrial packaging such as bags and supersacks, with a CoA and SDS per lot. Pricing depends on volume and packaging; request a current bulk quote with your quantity and ship-to.
What is the REACH and TSCA regulatory status of Isophthalic Acid (IPA)?
Isophthalic Acid (IPA) (CAS 121-91-5) is subject to U.S. TSCA Inventory requirements; supplying it into the EU requires valid REACH registration ((EC) No 1907/2006). RawSource cannot verify a third-party supplier's registrations — buyers should require documented TSCA and REACH compliance for their jurisdiction and volume (EC 204-506-4).