Application of Modified Amino Acid-Derived Diols as Chain Extenders in the Synthesis of Novel Thermoplastic Polyester–Urethane Elastomers

Owing to their robust processability and mechanical dexterity, thermoplastic polyurethanes (TPUs) have been utilized in a wide variety of applications from commodity to more niche biomedical applications. Despite this, the focus on deriving monomers from sustainable resources has been relatively low; however, bioderived diisocyanates, diamine/diol chain extenders, and polyester-based polyols have all been studied. Herein we report the application of biorenewable diol chain extenders derived from amino acids using an organocatalyzed process in bulk. To determine the effect of extender chain length on the properties of the resultant materials, TPEUs were synthesized using diol extenders derived from amino acids, 1-(1,3-dihydroxypropan-2-yl)-3-ethylurea (C_3u), 1-(1,4-dihydroxybutan-2-yl)-4-ethylurea (C_4u), and 1-(1,5-dihydroxypentan-2-yl)-5-ethylurea (C_5u). When poly­(ε-caprolactone) (PCL) and 1-isocyanato-4-[(4-isocyanatocyclohexyl) methyl]­cyclohexane (H₁₂MDI) were used as the polyol and diisocyanate, respectively, TPEUs were synthesized yielding materials with a predetermined percentage “hard segment” (%HS) and molecular weight. It was established through the selection of extender chain length and by controlling the %HS, that both the thermal and mechanical properties of the TPEUs could be controlled. Furthermore, the extender chain length was found to affect both the hydrophilicity and hydrolytic degradation profile of the resultant materials.