Polyurethanes are a broad class of polymers with excellent physical and mechanical properties, typically prepared from isocyanates and polyols. However, isocyanates are categorized as toxic and hazardous substances, which are under increasing regulatory scrutiny. A promising alternative is to prepare isocyanate-free polyurethanes by reacting cyclic carbonates with multifunctional amines. Previously, we prepared non-isocyanate polyurethanes from carbonated soybean oil (CSBO) and tested them as adhesives. They displayed excellent adhesive properties, but were elastomeric with relatively low softening points, near room temperature. The research was subsequently directed toward increasing rigidity and glass transition temperature (Tg) of the basic CSBO non-isocyanate polyurethanes network, while maintaining bonding characteristics. Increased rigidity and Tg was realized by inserting some small rigid, cyclic carbonates into the structure. Terephthaloyl and adipoyl bicyclic carbonate were selected as potentially good modifiers of CSBO and isophorone diamine (IPDA) was used as the best curing agent. The synthetic procedure involved partial reaction of CSBO and bicyclic carbonates with IPDA to obtain a prepolymer which was then applied to the bonding surfaces of aluminum and wood test coupons. Samples were cured at 110 °C for 2 hours. Bicyclic carbonates, as expected, increased stiffness of the resulting polyurethanes and produced rigid, very hard samples with higher glass transition temperatures. This approach demonstrates the potential to tailor final properties of non-isocyanate polyurethanes.
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