Enhancing the Tensile Behavior of HTCE Films Using β-Hydroxyethylurea as Chain Extender via a One-Step Solvent-Free Strategy

Multi-hydrogen bond chain extenders are widely used to improve the mechanical properties of polyurethane elastomers, but their incorporation often requires polar organic solvents, limiting solvent-free processing and large-scale production. Herein, a one-step solvent-free strategy was developed by dispersing β-hydroxyethylurea (2-Hu) in low-molecular-weight polyethylene glycol (PEG) to construct a mixed chain-extending system for hydroxyl-terminated polycaprolactone polyether (HTCE)-based polyurethane. Fourier transform infrared spectroscopy (FTIR) confirmed successful polyurethane formation, while small-angle x-ray scattering (SAXS) and low-field nuclear magnetic resonance (LFNMR) revealed that 2-Hu enhanced hydrogen bonding, promoted hard-domain aggregation, and strengthened microphase separation. Density functional theory (DFT) calculations demonstrated stronger intermolecular hydrogen-bonding interactions for 2-Hu than for 1,4-butanediol (BDO). Consequently, the crosslink density increased from 3.06 × 10⁻⁴ to 3.41 × 10⁻⁴ mol·mL⁻¹, and the tensile strength improved from 0.86 to 1.00 MPa. Moreover, the 2-Hu-containing polyurethane exhibited complete elastic recovery after 10 loading–unloading cycles, demonstrating excellent reversible deformation enabled by the dynamic hydrogen bonding network. This solvent-free strategy provides a simple and scalable route for preparing polyurethane elastomers containing multi-hydrogen bond interactions.