Metal-free synthesis of novel biobased dihydroxyl-terminated aliphatic polyesters as building blocks for thermoplastic polyurethanes

Using the organic compound 1,5,7-triazabicyclo[ 4.4.0]dec-5-ene (TBD) as a catalyst for step-growth polymerization, a series of well-defined hydroxyl-telechelic renewable aliphatic polyesters (including poly(1,3-propylene adipate); poly(1,4-butylene adipate); poly(1,12-dodecylene sebacate); and poly(1,2-dimethylethylene adipate), PDMEA) were synthesized and studied. PDMEA is a novel polyester, which has not been reported before. The results of 1H NMR and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry indicate that the polymers are fully hydroxyl terminated. From differential scanning calorimetry (DSC) thermograms, we found that the glass transition temperatures (Tg) of these polyesters are below ??20 ??C. Only a Tg but no melting peak is observed in the DSC curve of the novel PDMEA. This indicates that PDMEA, contrary to the other renewable polyesters, is totally amorphous. Furthermore, using hexamethylene diisocyanate and hexamethylene diamine, poly(ester urethane urea)s (PEUUs) based on PDMEA were successfully synthesized. The Tg of the prepared PEUUs is below 0 ??C, and no melting behavior of the soft-segment is observed. The PEUU, with a flow temperature of over 200 ??C, thus behaves as an elastomer at room temperature. Its mechanical properties, such as a relatively low tensile E-modulus (??20 MPa) at room temperature and a sufficiently high strain at break (??560%), make it suitable for use in, for example, biomedical applications.