Post-crosslinkable biodegradable thermoplastic polyurethanes: Synthesis, and thermal, mechanical, and degradation properties

Biodegradable thermoplastic polyurethanes (TPUs) with tuneable properties are of great interest in various applications. In this study, two kinds of poly(e-caprolactone) (PCL)-based biodegradable TPUs were synthesized using either DL-dithiothreitol (DTE) or glycerol as chain extenders. The reactive side groups on the chain extenders provide uniformly spaced post-crosslinking sites that can be bridged by thiol oxidation for DTE and by diisocyanate grafting for glycerol, thus leading to lightly crosslinked TPUs that can still be easily processed. The chemical structure, thermal properties, mechanical performance, and degradation behaviour of these TPUs were studied comprehensively. Their chemical structures were verified by nuclear magnetic resonance spectroscopy (H-1 NMR), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The post-crosslinldng hindered the crystallization of the PCL region and significantly enhanced the thermal decomposition temperature. Post-crosslinked TPUs achieved significant improvements in modulus, ultimate strength, flexibility, and tear resistance compared to their neat counterparts. The degradation rate was found to correlate with material wettability, and the formation of chemical crosslinks reduced the hydrolytic degradation rate of TPUs. In summary, by introducing functional groups via chain extenders and post-crosslinking, biodegradable TPUs with improved and tuneable properties and suitable for various applications could be obtained.