Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2010
Publication Date: 11/2/2010
Citation: Wyatt, V.T., Nunez, A., Strahan, G.D. 2010. The Lewis acid catalyzed synthesis of hyperbranched Oligo(glycerol-diacid)s in aprotic polar media. Journal of the American Oil Chemists' Society. 87:1359-1369.
Interpretive Summary: The production of biodiesel, an alternative diesel fuel produced from fats and oils, is projected to grow exponentially because it is a renewable fuel with improved exhaust emissions. With increased production of biodiesel; however, there also is an increased production of glycerol, the major co-product from the process used to produce biodiesel. Accordingly, there is a need to find new uses for glycerol. We previously demonstrated the potential of using glycerol to produce polymers. In this study, we demonstrated that polymers of glycerol and organic acids could be made more readily by conducting the reaction in selected solvents. The new strategy yielded products of increased chain length and branching, which are structural characteristics at the molecular level that influence the physical properties of the polymer. Such glycerol-based polymers are expected to render new biocompatible materials that have potential uses as cosmetics, food additives, surfactants, and lubricants. The development of new markets for glycerol should have a significant impact on the economics of biodiesel production, since increased credit for this co-product would improve the economics of biodiesel and make it more commercially competitive with petroleum-derived diesel.
Technical Abstract: The Lewis-acid, titanium (IV) butoxide (15% (w/w; catalyst/reactants)), was used to catalyze the condensation of 0.05 mol glycerol with 0.10 mol of either succinic acid, glutaric acid, or azelaic acid to produce oligomers. The reactions were refluxed in dilute solutions of dimethylsulfoxide (DMSO) or dimethylformamide (DMF) for 24 hours. The oligomers were obtained, on average, in 84% yield and were characterized by qualitative solubility studies, 1H NMR, 13C NMR, one dimensional and two dimensional NMR, MALDI-TOF mass spectrometry, and gel permeation chromatography (GPC). The synthesized oligomers had a number of average molecular weights (Mn) ranging from 2118 g/mol to 3245 g/mol, with degrees of polymerization ranging from 12.2 to 13.4 repeat units. The oligomers had low polydispersities (Mw/Mn) that averaged 1.33. Degrees of branching (DOB) varied from 25% to 80% and, like Mn and DOP, were dependent on the aliphatic chain length of the diacid. It was determined that some diacids were terminated with dimethylamine, generated from the hydrolysis of DMF, by as much as 36%.