CHDA (1,4-cyclohexanedicarboxylic acid) exhibits a unique combination of linear aliphatic and aromatic diacid character.
The performance of CHDA in polyester-melamine thermoset coatings has been well documented.
The factors selected for evaluation included: (1) level of CHDA in the diacid segment of a model polyester polyol, (2) effect of coating crosslink density on performance of a 1/1 molar CHDA/PIA polyol, and (3) polyester performance relative to commercially available acrylic controls.
The diacid segment was varied from 67% CHDA to 100% PIA.
Table 4 shows that CHDA reduces coating viscosity, but not quite as much as AD.
In impact testing, CHDA behaves like AD to greatly improve flexibility, whereas PIA alone is very brittle.
Stabilized coatings containing CHDA were lower in viscosity than the unstabilized ones.
Replacing PIA with any level of CHDA reduces the outdoor durability of the polyol in unstabilized coatings.
Polyols containing CHDA weathered better than those containing AD, especially at 50% substitution of the PIA.
In summary, CHDA lowers the viscosity of the PIA polyol similar to AD.
In polyester polyols for polyurethane coatings, CHDA strikes a balance in mechanical properties and outdoor durability.
Results showed that replacing 33-50 mole % of PIA with CHDA in the polyol improves coating flexibility, and maintains coating [T.