Synthesis and physical properties of mono-estolides with varying chain lengths

Abstract

Saturated mono-estolide methyl esters and enriched saturated mono-estolide 2-EH esters were synthesized from oleic and different saturated fatty acids under three different synthetic routes. Estolide numbers (EN), the average number of fatty acid units added to a base fatty acid, varied with synthetic conditions. The attempts at obtaining saturated mono-estolide 2-EH esters, EN = 1, via distillation proved to be challenging, which lead to estolide samples with EN > 1 and the pour point values followed the same trend as the high EN estolides. The other synthetic routes provided saturated mono-estolide methyl esters with EN = 1. The resulting pour point values showed a linear relationship between the saturated capping chain length and pour point. As the saturated capping chain length increased the pour points also increased (higher temperatures): C-2 capped −30 °C, C-10 capped −12 °C, and C-18 capped 3 °C. The saturated mono-estolide methyl ester viscosities also showed an increase in viscosity at 40 and 100 °C as the saturated chain lengths increased. The viscosities for the C-4 saturated mono-estolide methyl ester was 9.5 cSt at 40 °C and 2.6 cSt at 100 °C, while medium chain length derivations (C-10 saturated mono-estolide methyl ester) were 19.7 cSt at 40 °C and 4.2 cSt at 100 °C, and at the longer chain length derivations (C-18 mono-estolide methyl esters) were 27.6 cSt at 40 °C and 10.7 cSt at 100 °C. In general, a new series of saturated oleic mono-estolide methyl esters were synthesized and physical properties were collected. The physical property data indicated that both chain length and EN affect low temperature properties.