An aromatic diacid that upgrades unsaturated polyester and gel-coat resins to high-performance grades. 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.
▸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.
Physical Properties
Physical Description
Colorless solid; Sublimes without decomposition; Melting point = 347 deg C; Faintly beige powder
Appearance
Needles from water or alcohol
Boiling Point
Boiling point = 753.00 K (Based on predicted value for phthalic acid by Meissner's method with a suitable adjustment for isomerism based on similar compound relationships.)
Melting Point
Triple point temperature and pressure = 619.15 K (estimated to be equal to the melting point), 2.8020X10+3 Pa
Solubility
In methanol: 4.0 g/100 g at 25 °C; in propanol: 1.7 g/100 g at 25 °C, 2.7 g/100 g at 50 °C; in glacial acetic acid: 0.23 g/100 g at 25 °C
Density
1.54 at 25 °C
Vapor Pressure
VP: 0.009 Pa at 100 °C
LogP
log Kow = 1.66
Autoignition Temperature
700 °C
Viscosity
0.00025186 Pa-s at 619.15K (346 °C)
Heat of Vaporization
1.0921X10+8 J/kmol at the melting point of 619.15 K (346 °C)
Surface Tension
0.048239 N/m at 346 °C
Dissociation Constants
pKa1 = 3.70; pKa2 = 4.60 at 25 °C
Safety & Handling
Full SDS available on request
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.
HS / Tariff Classification
🌐Harmonized System (HS) Code — 6-digit international heading
2917.39
Chapter 29
Organic chemicals
Heading 29.17
Internationally harmonized (WCO HS)
Subheading 2917.39
6-digit international code — national tariff line adds further digits
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.
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.
Disclaimer. Information on this page — including properties, identifiers, hazard, transport (DOT/UN) and tariff (HS) classifications, and applications — is provided for general reference and is compiled from authoritative public sources (e.g. PubChem/ECHA, 49 CFR 172.101, the Harmonized Tariff Schedule). Values are typical and are not a guaranteed specification; the Certificate of Analysis (CoA) for the lot purchased governs. Products are sold for industrial and professional use only. Nothing here is a medical, health, or efficacy claim or advice. Always consult the current Safety Data Sheet (SDS) before handling, storage, transport or disposal, and confirm regulatory status, classification and suitability for your application and jurisdiction. Hazard, transport and tariff classifications must be verified for your specific shipment. RawSource makes no warranty, express or implied, and assumes no liability for use of this information. Trademarks. Third-party trademarks and brand names are the property of their respective owners; any reference is nominative — used only to identify a comparable product — and does not imply affiliation with, sponsorship by, or endorsement by the trademark owner.
Ready to Source Isophthalic Acid (IPA)?
Our procurement team handles specification confirmation, lead time, and logistics.
