Novel biobased polyurethanes were synthesized from rubber seed oil (RSO), a renewable resource. The RSO monoglyceride, together with xylene and hexamethylene diisocyanate (HMDI), was employed to synthesize the desired urethane-based prepolymer with isocyanate (NCO)-terminated end groups followed by curing. The degrees of crosslinking of the polyurethane after curing were assessed with their swelling behavior. The properties of the resulting polyurethanes were found to be dependent on the type of diisocyanate and their molar ratios to the RSO monoglyceride. The network structures, which were assessed through swelling studies, showed that networks based on HMDI with an NCO/OH ratio of 1.50 were better crosslinked than with those toluene diisocyanate. The thermal properties of the samples analyzed by thermogravimetric analysis showed two and three decomposition stages in aliphatic- and aromatic-based RSO polyurethanes, respectively. The highest stability with initial decomposition temperature (253 degrees C) and percentage residual at 500 degrees C (11.4%) was achieved with an aliphatic-based RSO polyurethane. (C) 2008 Wiley Periodicals, Inc.