Synthesis and physical properties of cuphea-oleic estolides and esters

Cuphea-oleic estolides and esters were synthesized from cuphea and oleic FA with various amounts of perchloric acid (0.01 to 0.40 equiv) at 60°C. Estolide yields ranged from 30 to 65% after Kugelrohr distillation. Estolide number (EN), the average number of FA units added to a base FA, varied with reaction conditions. Cuphea-oleic estolides were esterified with 2-ethylhexanol to obtain high yields of the corresponding ester. A streamlined, one-pot process was used to synthesize the estolide and its ester with 0.05 equiv of HClO₄, with, esterification incorporated into an in situ second step to provide a functional fluid at a very reasonable cost. The physical properties of the cuphea-oleic estolides and estolide esters, including their viscosities, pour points, and cloud points, were related directly to the amount of oligomerization (EN), i.e., viscosity increased with higher oligomerization. The viscosity index ranged from 132 to 166 cSt for the free-acid estolides, whereas the complex estolide 2-ethylhexyl esters had slightly high viscosity indices that ranged from 165 to 181 cSt. These new cuphea-oleic estolide esters displayed good low-temperature properties (pour point −42°C and cloud point −41°C).