Silicone Structurants for Soybean Oil: Foams, Elastomers, and Candles

Soybean oil-derived polyurethanes, while much greener than those derived from isocyanates, have a problematic combustion profile; concerns exist about the nitrogen-containing compounds found in the smoke. Silicones typically burn cleanly to form an insulating silica layer upon combustion. We have examined the ability of silicones to convey improved thermal stability to soybean oil. The oil was modified via an ene reaction to incorporate an alkoxysilane functionality that was used in a subsequent Piers-Rubinsztajn reaction with silicones to create foams and elastomers. Cross-linked materials with densities ranging from similar to 0.6 to 0.9 g/mL and containing up 76% by weight soybean oil were prepared. The addition of varying amounts of a linear PDMS chain extender allowed for control of the modulus (0.04-0.32 MPa). Cross-linking rapidly occurred, <60 s for full cure. Foams were produced without the need for external blowing agents, due to the generation of methane as a byproduct of the Piers Rubinsztajn reaction. The soybean oil/silicone materials burned cleanly and without dripping, as shown in particular with the elastomer containing 76 wt % soybean oil. The external surfaces of the objects, after combustion, were rigid silica-rich structures.