Hydrogen-bond regulation of maleimide-terminated polyurethane via alkaline lignin for balanced mechanical and anti-corrosion properties

A synergistic two-step strategy integrating molecular end-capping with biomass filler reinforcement was developed to overcome the inherent trade-offs among mechanical strength, water resistance, and corrosion protection in polyurethane (PU) coatings. Maleimide end-capping agents with different structures were systematically screened, and 4-hydroxyphenylmaleimide (4-HPM) was identified as optimal, yielding the highest hydrogen-bonding index (HBI = 4.11) and balanced mechanical properties (tensile strength of 14.70 MPa and elongation at break of 1412%). Alkaline lignin (AL), an industrial by-product from pulping processes, was then introduced as a renewable hydrogen-bond reinforcing filler into the 4-HPM-capped PU matrix. At an optimal loading of 1wt.‰, AL achieved uniform dispersion and provided supplementary hydrogen-bonding sites, increasing crosslinking density and hard-segment order. The resulting composite (PUM-1) exhibited a tensile strength of 30.44 MPa, an elongation at break of 1232%, a water contact angle of 84.7°, and a low-frequency impedance modulus of 1.94 × 10 10  Ω·cm 2 , with long-term stability in salt spray tests. Excessive AL loading (≥5wt.‰) caused aggregation and hydrophilic defects, disrupting the network. Notably, maximization of structural parameters (HBI = 5.55) did not translate to optimal corrosion protection; balanced dispersion and crosslinking uniformity governed long-term performance. This work establishes quantitative design rules for biomass-reinforced high-performance anticorrosion coatings.