Polyurethanes are a versatile class of polymers formed by the reaction between polyols and isocyanates. Depending on the structure and molecular weight of the polyol as well as the cross-link density of the network, a wide range of materials such as rigid plastics, flexible foams, liquid coatings, and thermal insulators can be produced. Polyurethanes typically contain hard and soft segments that contribute to their thermomechanical properties. The hard segments, usually the isocyanate and chain extender portions, are below their T_g at room temperature and contribute to the mechanical strength, thermal stability, and solvent resistance of the network. The soft segments, typically the polyol portion, are above their T_g at room temperature and control the elasticity, flexibility, and impact resistance of the network. Polyurethane binders, useful in adhesives, sealants, and coatings applications, can be prepared through the use of hydroxyl-terminated polybutadiene (HTPB) as the polyol component and methylene diphenyl diisocyanate (MDI) or toluene diisocyanate (TDI) as the isocyanate (hard) component. Although HTPB is widely used as a component of polyurethane binders, the polyol suffers from high viscosity while the networks exhibit low thermo-oxidative stability due to the presence of residual alkenes. Moreover, HTPB is synthesized from unsustainable petroleum sources. Herein, we report the synthesis of hydroxyl-terminated polymers from an array of biosynthetic monomers through [Ru]-catalyzed olefin metathesis. The thermomechanical properties of these materials were studied by techniques including differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and rheology. Cure protocols for these materials were developed and polyurethane networks were prepared. The mechanical properties of polyurethane bars were measured via dynamic mechanical analysis (DMA) and tensile testing. This allowed us to explore structure/property relationships for bio-based polyurethanes and optimize formulations and cure protocols to maximize mechanical properties while maintaining low T_gs.

Cristian Zavala

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