Performance of CHDA in Polyester Polyols for Weatherable 2K Polyurethane Coatings

By Stacey J. Marsh

Polyurethane are known for their durability and overall good balance for mechanical properties. Both acrylics and polyesters are used as polyols in two-component, solventborne polyurethane coatings. Polyester polyols containing isophthalic acid (PIA) weather extremely well, but they have poor flexibility. Usually, a combination of a flexible diacid, such as adipic acid (AD), and PIA are used to achieve a hardness/flexibility balance in the coating.

While improving flexibility, AD has an adverse effect on the beneficial properties of PIA, especially outdoor durability. CHDA (1,4-cyclohexanedicarboxylic acid) exhibits a unique balance of properties that are characteristic of linear aliphatic and aromatic diacids. These properties in­clude rapid reactivity, a hardness/flexibility balance, and resistance to chemicals and humidity.

The objective of these experiments was to evaluate the performance, particularly outdoor durability, of high-solids, two-component, pigmented polyurethane coatings containing CHDA. Experimental variables included the CHDA/PIA molar ratio in a model polyester polyol, coat­ing crosslink density, and effect of a commonly used ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) package.

Comparisons were made to control polyester polyols containing AD/PIA and commercially available acrylic polyols marketed for exterior A) and hindered amine light stabilizer (HALS) package. Comparisons were made to control polyester polyols containing AD/PIA and commercially available acrylic polyols marketed for exterior applications.