Synthesis, Crystallization, and Melting Behavior of Metathesis-like Triacylglycerol Oligomers: Effects of Saturation, Isomerism, and Size

Oligomers of triacylglycerols (TAGs) are derived from the self-metathesis of vegetable oils and are sought for a variety of applications, in particular waxes. A series of model dimers and quatrimers of TAGs with controlled structures were synthesized and characterized by ¹H NMR and ¹³C NMR. Their thermal stability, crystallization, and melting behavior were investigated using TGA and DSC. The relationship of oligomeric structure to thermal properties was found to adhere well to predictive trends. Although the effect of saturation on the phase behavior was the most dramatic, with differences in crystallization temperature up to 62 °C, isomerism and molecular mass were shown to affect crystallization significantly, leading to differences of up to 30 °C. The findings of the study show that the thermal parameters of the oligomers can be adjusted in a very broad range by saturation, isomerism, and size, making the development of a large variety of biosourced functional lubricants and waxes possible

Synthesis and Physical Properties of Triacylglycerol Oligomers: Examining the Physical Functionality Potential of Self-Metathesized Highly Unsaturated Vegetable Oils

Seven model oligomers (from dimer to octamer) of the triacylglycerol (TAG) triolein were synthesized from oleic acid and fully characterized by ¹H NMR, ¹³C NMR, mass spectroscopy, and gel permeation chromatography (GPC). The thermal stability of the oligomers as determined by TGA was excellent, with degradation beginning at 342 °C for the most thermally labile samples. The samples all presented glass transitions at low temperatures, with <i>T</i>_g continuously shifting to higher temperatures with increasing numbers of monomers. The crystallization and melting behavior scaled with molecular size and relative number of double bonds in the trans- configuration. Flow behavior was investigated over a large range of temperatures (−10 to 110 °C), and application of the Herschel–Bulkey model to shear stress versus shear rate data evidenced a flow behavior dependent on molecular size and temperature. The oligomers presented a thinning to Newtonian flow transition temperature proportional to molecular size. The viscosity versus temperature data, fitted with a generalized van Velzen equation, suggested that it is the competition between the trans- character and size of the molecules which determines the rheology of these molecules. Overall, all the investigated properties plateaued at the hexamer, suggesting that no further marginal utility can be obtained with larger oligomers

Lubricating and Waxy Esters, V: Synthesis, Crystallization, and Melt and Flow Behaviors of Branched Monoesters Incorporating 9‑Decenol and 9‑Decenoic Acid

Branched derivatives of waxy monoesters incorporating 9-decenol and 9-decenoic acid were synthesized using epoxidation and ring-opening esterification. The reactions were conducted at two different temperatures and monitored over time. The crystallization, melting, and viscosity of the compounds were all controlled strongly as a function of incremental branching. Isomerism was shown to be critically important: an OH group at the end of the hydrocarbon chain completely suppressed crystallization, whereas its isomer with a terminal acyl chain did not. The structure of the linear monoesters were shown to provide the templates for crystallization, melting, and flow behavior, whereas the branching effect extended but could not erase the effect of the base molecular architecture. These compounds present a large range of properties that are suitable for a variety of applications ranging from waxes to lubricants

Lubricating and Waxy Esters. 6. Synthesis and Physical Properties of (<i>E</i>)‑Didec-9-enyl Octadec-9-enedioate and Branched Derivatives

A fatty aliphatic “Jojoba-like” ester, didec-9-enyl octadec-9-enedioate, was synthesized by Steglish esterification, and C3-branched derivatives were prepared from its epoxide by a solvent-free epoxide ring-opening and one-pot normal condensation reaction. The thermal stability, phase transition behavior, solid fat content, and flow behavior were investigated using thermogravimetric analysis, differential scanning calorimetry, p-NMR, and rotational rheometry, respectively. These properties were predictably varied as a function of branching, explained by the combined effects of mass, hydroxyl groups, and geometric steric hindrances imposed by the protuberant branches. The compounds demonstrated high thermal stability (>230 °C), competitive flow characteristics (210–773 cP at 40 °C and 31–66 cP at 100 °C) and superior low-temperature performance properties (−27 to −70 °C) suitable for exploitation in various applications such as lubricants, cosmetics, and pharmaceuticals

Lubricating and Waxy Esters. 4. Synthesis, Crystallization Behavior, Melt Behavior, and Flow Behavior of Linear Monoesters Incorporating 9‑Decenol and 9‑Decenoic Acid

Three pure jojoba wax-like esters (JLEs), i.e., octadec-9-enyl dec-9-enoate (JLE 28₁), dec-9-enyl oleate (JLE 28₂), and dec-9-enyl dec-9-enoate (JLE-20), were synthesized from fatty acids and fatty alcohols. Calorimetric, solid fat content evolution, and flow data were used to elucidate the phase behavior of the JLEs. It was clearly established that the length of the terminal alkyl chain and orientation of the linking group in the side chains of the bent-core molecules play an important role in the phase development of the JLEs and ultimately their physical properties. Measurable differences in all physical properties investigated were detected between the isomers based on the position of the ester group in the molecule, leading to informed choices on what isomer should be synthesized for similar monoesters for specific applications

Lubricating and Waxy Esters II: Synthesis, Crystallization, and Melt Behavior of Branched Monoesters

A comprehensive study of branched derivatives of four pure jojoba wax-like esters (JLEs), having 36, 40 (two isomers), and 44 carbons was conducted to elucidate their crystallization and melting behavior. Crystallization and melting characteristics depended strongly on the number of branches, molar mass, and symmetry. The derivatives demonstrated a very strong tendency to form glassy liquids rather than crystal phases and remain liquid-like at very low temperatures. As the number of branches increased, their crystallinity decreased drastically while their glassy phase increased concomitantly with the depression of the onset of crystallization and/or glass transition temperature. A variety of possible transformation paths, ranging from very little polymorphic activity to extremely polymorphic behavior, depending on number of branches, mass, and symmetry were revealed. It is shown that asymmetry plays a large role in the low temperature behavior, rendering the branched derivatives of the asymmetrical JLEs much better candidates for lubricant formulations