Isophthalic acid resins

Isophthalic acid is one of the key building blocks of high-quality unsaturated polyester resins. By using isophthalic acid instead of phthalic anhydride in the resin backbone, resin producers create so-called iso resins with better mechanical strength, water resistance and chemical resistance. AOC offers a broad range of isophthalic resins for gelcoats, marine laminates, tanks, pipes and CIPP.

What does isophthalic acid do in a resin?

Isophthalic acid (sometimes misspelled as isophtalic acid) is an aromatic dicarboxylic acid. In a polyester backbone it creates longer, more regular polymer chains with fewer weak spots for hydrolysis. The result is a cured resin that absorbs less water, keeps its properties longer and handles higher temperatures and mild chemicals better than a standard ortho resin.

When isophthalic acid is combined with neopentyl glycol (NPG), the performance rises further. These Iso/NPG resins are widely used as gelcoat bases and in demanding outdoor and anti-corrosion applications.

Isophthalic vs orthophthalic resins

Orthophthalic resins are cost-effective, versatile and easy to process. They are well suited to general laminating, casting and many tank and pipe applications. Isophthalic resins are the step up when the part faces water immersion, weathering or chemical exposure over a long service life.

• Choose ortho for general-purpose laminates, artificial stone, casting and cost-driven parts.
• Choose iso for boats, swimming pools, gelcoats, tanks, pipes and CIPP liners that need hydrolysis resistance.
• Choose Iso/NPG for gelcoats and parts that need superior weathering and colour stability.

Examples of AOC isophthalic resins

Our portfolio covers most processes. Synolite™ 0288-I-2 and 0288-L-1 are isophthalic hand lay-up and spray-up resins for marine use with Lloyd's and RINA approval. Palatal® A 400 TV-42 combines hydrolysis resistance with low water absorption. Synolite™ 1717-N-1 targets high-performance tanks and pipes, while Synolite™ 7412-G-1 is designed for RTM and infusion.

Next™ iso and ortho options

Customers looking for a lower footprint can choose products carrying the Next™ label. This label marks AOC products with a defined sustainability benefit, such as recycled or bio-circular feedstock, styrene-free chemistry or reduced emissions. Within our ortho and iso ranges, rPET-based formulations and styrene-free alternatives such as Beyone™ 417-N-01, a flexible styrene-free isophthalic resin, help customers reduce their impact without losing performance.

Getting the most from isophthalic acid resins

The benefit of isophthalic acid only shows when the resin matches your process and end use. AOC Technical Service helps you compare iso, ortho and Iso/NPG options, run trials and fine-tune your process. Download the Product Selector Guide or get in touch with our experts to find the isophthalic resin that fits your application.