First-principles investigation of electron trigger mechanism in conductive polyurethane grafted with conjugated polymers

Abstract Polyurethane (PU) coatings provide mechanical robustness and weather resistance for wind turbine blades but suffer from inherent electrical insulation, which promotes surface charge accumulation and increases lightning strike vulnerability. Rendering PU electrically conductive is therefore a promising strategy to mitigate this risk. In this study, we employ density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level to investigate PU hard segments (MDI-BDO) grafted with three conductive polymers: polyaniline (PANI), polypyrrole (PPy), and pyrrole-3-carboxylic acid-functionalized polythiophene (PTh). The isocyanate (-NCO) group is identified as an efficient “electron trigger” that initiates a cascade from covalent bonding to electronic state redistribution. Grafting substantially modifies the electronic structure: the HOMO-LUMO gap narrows from 5.28 eV for pure MDI-BDO to 2.24 eV for MDIBDO-g-PANI, compared with 4.12 eV and 4.11 eV for the PPy and PTh systems, respectively. The PANI-grafted system achieves the strongest interfacial binding of 146.4 kJ/mol, the highest polarizability of 1306.6 a.u., and the largest vibrational entropy of 549.8 cal·mol⁻1·K⁻1. The characteristic -NCO IR stretching mode at approximately 2448 cm-1 disappears in all grafted systems, confirming covalent bond formation, while Raman spectra reveal signatures consistent with narrow-gap semiconducting behavior. Among the three systems, MDIBDO-g-PANI exhibits the optimal combination of strong interfacial binding, narrow energy gap, and continuous density of states distribution. The present theoretical predictions establish a structure-activity relationship linking interfacial chemistry, electronic structure, and charge dissipation capability, providing a computational foundation for the rational design of conductive PU-based coatings with potential applications in lightning protection.