Synthesis of Chain Extender via Baylis–Hillman Reaction for Postmodification of Polyurethane Hard Segment Domains

Polyurethane, as a highly adaptable polymeric precursor, plays a pivotal role in a wide range of advanced applications, particularly in biomedical engineering, regenerative medicine, and multifunctional material design. The Baylis–Hillman reaction synthesized a multifunctional chain extender that provided a suitable platform for postmodification of the polyurethane. Therefore, this study aims to engineer unsaturated hard domains tailored for postsynthetic modifications by designing and synthesizing a novel chain extender through the Baylis–Hillman reaction. The postpolymerization of unsaturated hard domains was accomplished via thiol–ene chemistry as a clickable reaction. This was accomplished by modifying gelatin with γ-thiobutyrolactone, which subsequently served as one of the reactants in the thiol–ene reaction. The influence of the hard segment content on the thiol–ene reaction was systematically investigated to optimize the fabrication of cross-linked gelatinized polyurethane films, highlighting its critical role in controlling the network architecture and mechanical properties. Interestingly, the results demonstrated that the hard segment content plays a pivotal role in governing the formation and extent of cross-linking in the synthesized polyurethane networks. Attenuated total reflection infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance (NMR) confirmed the successful synthesis of an unsaturated-chain extender and incorporation into the polyurethane backbone. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and atomic force microscopy (AFM) were employed to investigate the effect of hard segment content on the formation of cross-linked gelatinized-polyurethane films. Mechanical analysis revealed a direct correlation between the hard segment content and the cross-link density of the synthesized samples. Furthermore, X-ray photoelectron spectroscopy (XPS) confirmed surface composition variations in the polyurethane films upon the incorporation of thiolated gelatin.