Synthesis and Characterization of Polyurethane Networks Derived from Soybean-Oil-Based Cyclic Carbonates and Bioderivable Diamines

Nonisocyanate polyurethane (NIPU) thermoset networks were produced from a novel soybean-oil-derived poly(vinyl ether) (i.e., poly[(2-vinyoxy)ethyl soyate]) possessing cyclic carbonate functional groups in the fatty acid ester side chains of the polymer. Three different linear aliphatic diamines, namely, 1,6-hexamethylenediamine, 1,9-nonanediamine, and 1,13-tridecanediamine, were used to cross-link the cyclic carbonate-functional poly[(2-vinyoxy)ethyl soyate] [C-poly(2-VOES)]. All three of these diamines can be readily obtained from renewable resources. For comparison purposes, analogous NIPU networks were produced using cyclic carbonate-functional soybean oil (CSBO) in place of the C-poly(2-VOES). The chemical, thermal, viscoelastic, and mechanical properties of the six NIPU networks were characterized. With regard to the chemical nature of the soy-based, carbonate-functional component, it was found that the polymeric nature of C-poly(2-VOES) resulted in very different NIPU properties compared to analogous cross-linked networks based on CSBO. While the CSBO-based NIPU networks exhibited lower Young’s moduli and ductile behavior, the networks based on C-poly(2-VOES) showed significantly higher Young’s moduli and brittle behavior. In addition, measurements using dynamic mechanical analysis showed significantly high cross-link densities for the networks based on C-poly(2-VOES), which can be attributed to a much higher number of methine carbon atoms per molecule in C-poly(2-VOES) as compared to CSBO. In addition to the cross-links resulting from the reaction of the amine groups of the cross-linker with the cyclic carbonate groups of the soy-based carbonate-functional materials, these methine carbon atoms serve as cross-links in the NIPU networks. The higher cross-link densities achieved with the use of C-poly(2-VOES) explain the thermal and mechanical property differences observed between networks based on the two different soy-based carbonate-functional materials. With regard to the influence of the diamines on NIPU network properties, as expected, increasing the chain length of the diamine cross-linker decreased cross-link density, which, in general, resulted in decreases in Young’s moduli and glass transition temperature.