Synthesis of levulinic acid–glycerol ketal–ester oligomers and structural characterization using NMR spectroscopy

• Published in: European polymer journal 2011-12, Vol.47 (12), p.2451-2457
• Main Authors: Amarasekara, Ananda S., Hawkins, Steven A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Catalysis; Catalysts; Chlorides; Exact sciences and technology; Glycerol; Glycerols; Heating; Levulinic acid; NMR spectroscopy; Oligoester; Oligoketal; Oligomers; Organic polymers; Physicochemistry of polymers; Polycondensation; Preparation, kinetics, thermodynamics, mechanism and catalysts; Renewable resources
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2011.09.007

Oligomerizations of renewable resources based monomers levulinic acid, and glycerol were studied using three different catalysts, Sb 2O 3, p-toluenesulfonic acid, and 1-(1-propylsulfonic)-3-methylimidazolium chloride. The highest average degree of oligomerization of 9.8 was achieved by heating an equimolar mixture of levulinic acid, and glycerol first from 23 to 210 °C under a nitrogen atmosphere for 1 h, and then at 210 °C under a vacuum for 9 h, in the presence of 1.0 mol% Sb 2O 3 catalyst. p-Toluenesulfonic acid, and 1-(1-propylsulfonic)-3-methylimidazolium chloride catalyzed reactions gave oligomers with relatively lower molecular weights. These levulinic acid–glycerol oligomers are shown to have ketal and ester links in a linear oligomer chain by using 1H and 13C NMR spectroscopy. Three different types of terminal units: keto, glycerol-ketal, and glycerol-ester were identified with the help of model compounds, and their relative percentages were calculated using quantitative 1H and 13C NMR data.