Linseed and soybean oil-based polyurethanes prepared via the non-isocyanate route and catalytic carbon dioxide conversion

Abstract

Soy- and linseed oil-based polyurethanes were prepared without using isocyanate monomers by curing carbonated soybean (CSBO) and linseed (CLSO) oils with different diamines. The conversion of the epoxidized seed oils with carbon dioxide to form cyclic carbonates was catalyzed with tetra-butylammonium bromide (TBAB) and silica-supported 4-pyrrolidinopyridinium iodide (SiO₂–(I)), which was readily recovered without requiring the conventional purification by solvent extraction of TBAB. Carbonate formation was monitored as a function of catalyst type and pressure, indicating slower conversion rates for the supported catalyst. Quantitative epoxy conversion was achieved and the amount of immobilized carbon dioxide increased from 15.2 wt% for CSBO to 19.6% for CLSO. The seed oil carbonates with variable carbonate content (20.2 to 26.8 wt%) were cured with 1,2-ethane diamine (EDA), 1,4-butane diamine (BDA) and isophorone diamine (IPDA) in order to examine the thermal and mechanical properties of the resulting non-isocyanate polyurethanes (NIPU). In contrast to the flexible conventional CSBO/EDA-NIPU, it was possible to increase NIPU glass transition temperatures from 17 °C to 60 °C and to improve stiffness, as expressed by Young's modulus, by three orders of magnitude. Higher crosslink densities accounted for reduced water swelling and toluene uptake.