Renewable polyol obtained by microwave-assisted alcoholysis of epoxidized soybean oil: Preparation, thermal properties and relaxation process

Abstract

The soybean oil polyol (SOP) use as feedstock in the polyurethane industry has been recently emphasized due to its excellent resistance to hydrolysis, which is also applicable in coatings and thermal insulation. In this article, the SOP was obtained by a very fast microwave-assisted alcoholysis of epoxidized soybean oil (ESO). The preparation method, thermal properties, and relaxation process were evaluated. High yields as opening and consumption epoxy group and selectivity of 99.8 mol%, 98.5 mol%, and 71.2 mol% were obtained. Through titrations, nuclear magnetic resonance and gel permeation chromatography were identified parameters as 0.32 mg KOH·g−1 acid number, 190 mg KOH·g−1 hydroxyl number, 150 mg KOH·g−1 saponification index, 0.17 wt% water content, 1463 g·mol−1 molecular weight, 4.98 average functionality, 2.4 × 10−5 mPa·s−1 viscosity at 333 K and 1.00 g·cm−3 density. The dielectric relaxation spectroscopy allowed identifying the α-relaxation process with a 193.5 K glass transition (Tg), 63.2 fragility index and 234.1 kJ mol−1 activation energy associated with Tg from the dynamic fragility index. The ionic conductivity temperature dependence on SOP obeys Arrhenius behavior. In summary, the SOP structure and thermal relaxation parameters determination are fundamental for the understanding of the structure-properties relationship of renewable polyurethanes.