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 H-1 NMR, C-13 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 degrees C for the most thermally labile samples. The samples all presented glass transitions at low temperatures, with T-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 degrees 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.