Branched Biobased Diesters with Exceptional Low Temperature and Flow Properties for Use in Lubricant Formulations

A vegetable oil based diester (1,6-hexyldioleate) was branched with propanoic acid (C3) using a green synthetic approach involving solvent- and catalyst-free epoxide ring opening followed by in situ normal esterification. A total of three branched ester derivatives possessing varied numbers of internal protruding branched ester and hydroxyl groups were obtained. All of the pure branched derivatives were comprised of mixtures of positional and/or stereoisomers. Differential scanning calorimetry showed that, regardless of the compositional inhomogeneity of each branched derivative, crystallization was suppressed completely in all of the branched compounds and they all demonstrated glass transitions below −65 °C. This unique thermal behavior is attributed to the internal protruding branched moieties and hydroxyl groups which dramatically slowed mass transfer. The viscosity of the branched compounds was 1 order of magnitude larger than that of the starting diester due to the increased resistance to flow associated with increased branching and hydrogen bonding introduced by the OH groups. Overall, these branched diesters demonstrated superior low temperature and flow properties comparable to existing nonsustainable commercial lubricants and analogous biobased materials, making them suitable alternatives for use in lubricant formulations, particularly in high performance industrial gear and bearing biolubricants.