Soybean Oil Based Isocyanates: Synthesis, Characterizations and Polymerizations
Isocyanates are valuable compounds that are used widely in many application areas of polymer industry. The most important area of use of isocyanates is to synthesize polyurethanes and polyureas. Important isocyanates, used in the polyurethane manufacturing, are 2, 4-toluene diisocyanate (2,4TDI), 2, 6-toluene diisocyanate (2,6TDI), 4, 4’-diphenyl methane diisocyanate (MDI), 1, 6 hexamethyl diisocyanate (HMDI), xylene diisocyanate (XDI), and isophorone diisocyanate (IPDI), all of which are petroleum derived [1-3].
Isocyanates can be synthesized in many ways. The Curtius, Hoffman and Lossen rearrangements, which may involve nitrene as an intermediate, are not succesful for large scale operations [4].
Literature search reveals a number of bio-based polyurethanes. In almost all of them, castor oil was used as a polyol source and petroleum based isocyanates were used as the isocyanate [5-12]. There are no examples where the isocyanate is bio-based. With the simple synthesis described in this work it is possible to obtain polyurethanes where both the isocyanate and polyol are bio-based.
In the first strategy, soybean oil isocyanates were obtained by substitution reaction between allylically brominated soybean oil and AgNCO [13]. In the second strategy, soybean oil was reacted with iodine isocyanate reagent [14-15]. Addition of iodo isocyanate to plant oils gives valuable intermediates. Similar to thiocyanogen addition, just one mole iodo isocyanate can be added to one mol of polyunsaturated fatty acids. This means that one mole unsaturated plant oil triglyceride can bind around three mol iodo isocyanate easily. Many positional isomers are obtained at the end of the both reaction. The products are valuable intermediates to synthesize poly-urethanes and poly ureas.
Synthesized soybean oil isocyanate and iodo isocyanate were polymerized with castor oil and glycerol. Castor oil and glycerol polyurethane of soybean oil iodo isocyanate showed tensile strength of 140 KPa and 270 KPa respectively. On the other side, polyurethanes of soybean oil isocyanate with same triols showed tensile strength of 100 and 125 KPa respectively
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