Isocyanate Reduction by Epoxide Substitution of Alcohols for Polyurethane Bioelastomer Synthesis

A phosphate ester-forming reaction was carried out by mixing epoxidized soybean oil with up to 1.5% o-phosphoric acid. In situ oligomerization took effect almost instantly producing a clear, homogeneous, highly viscous, and a low-acid product with a high average functionality. The resulting epoxide was used as a reactant for urethane bioelastomer synthesis and evaluated for rigid foam formulation. Results have shown that with a number of catalysts tested phosphoric acid significantly enhances a solvent-free oxirane ring cleavage and polymerization of the epoxidized soybean oil via phosphate-ester formation at room temperature. The resulting phosphoric acid-catalyzed epoxide-based bioelastomer showed an 80% decrease in extractable content and increased tensile strength at the same isocyanate loading relative to the noncatalyzed epoxide. The oligomerized epoxidized soybean oil materials exhibited ASTM hydroxyl values 40% less than the nonoligomerized starting material which translates to reduced isocyanate loadings in urethane applications. 1. Introduction Polyurethane elastomers and industrial foams manufacturing rely significantly on fossil fuels and their derivatives as major reactants for the production of polyols. Nonrenewable resources are rapidly being exhausted, therefore, a growing worldwide research effort is focused on the understanding and using renewable resources to reduce dependence on petroleum-derived materials and to develop innovative technologies and competitive industrial products. Vegetable oils such as soybean oil (SBO) are increasingly replacing petroleum-derived products owing to its environment-friendly, biodegradable, and noncorrosive properties [1–3]. Although SBO-based polyols have shown promising results in the production of urethane-formulated products ranging from elastomers to flexible foams [3–5], replacement of substantial portions of polyol and isocyanate with soybean oil-derived epoxides is economically significant. SBO-derived epoxides which include epoxidized soybean oil (ESBO) and bodied ESBO are intermediates in much of the chemistry to create soy-based polyols [4, 6–8], and so they are less expensive than many soy-based polyols. High reactivity through cleavage of the oxirane ring makes epoxides very versatile both as chemical intermediates and as end product. Epoxides are able to directly react with water to diols, with carboxylic acids to ester alcohols, and with alcohols to ether alcohols [9]. Moreover, epoxides have been reported to react with and partially displace isocyanate in urethane mixtures [6, 10, 11];