Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2011
Publication Date: 3/1/2011
Citation: Wyatt, V.T., Strahan, G.D., Nunez, A., Haas, M.J. 2011. Characterization of thermal and mechanical properties of oligo(glycerol-glutaric acid)s. Journal of Biobased Materials and Bioenergy. 5(1):92-101. Interpretive Summary: Recent legislative energy initiatives have promoted the expanded usage of renewable fuels as a means of decreasing our dependence on imported oil. One such renewable fuel is biodiesel, a diesel fuel alternative that is produced from agricultural fats and oils. 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 have previously demonstrated the potential of using free glycerol to make pre-polymers composed of glycerol units that can be further reacted to produce randomly branched polymers and oligomers in the presence and absence of solvent. In this study, we determine the thermal, physical and mechanical properties of these materials. Such glycerol-based materials are expected to render new biocompatible polymers that are of interest for potential uses as cosmetics, food additives, surfactants, and lubricants. The development of new markets for glycerol also would 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: Dibutyltin oxide was used to catalyze the synthesis of oligo(glycerol-glutaric acid)s in the absence and presence of solvent. Reaction times were either 10h or 24h for reactions performed in DMF and 24h for the neat reaction. The oligomers were obtained on average in 84% yield and were characterized by qualitative solvent solubility studies, proton NMR, Carbon 13 NMR, MALDI-TOF mass spectrometry, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The materials synthesized in solution had considerably lower number average molecular weights (g/mol) of 1050 (10h) and 1474 (24h) but higher polydispersity indexes [PDI (weight average molecular weight/number average molecular weight)] of 21.1 (10h) and 30.5 (24h) than the corresponding neat-derived material (number average molecular weight = 445,000; PDI = 5.8). Degrees of polymerization averaged 5.7 (10h) and 8.8 (24h) for the solvent-derived products compared to 2392.5 for products synthesized in the absence of solvent. Viscosity, glass transition temperature, change in heat capacity ('Cp), and molecular weight increased with reaction time and degrees of branching (DOB). DOBs were lower for the solvent-derived materials (41% (10h); 45% (24h)) than observed for material synthesized in the absence of solvent (82%). DOB and number average molecular weight largely account for the drastic physical and mechanical differences observed among materials synthesized in solvent and solvent-less systems.