Crosslinking and Mechanical Characterization of Hydroxyl‐Terminated Caprolactone‐Modified (Meth)acrylic Clearcoats for Automotive Applications

ABSTRACT Two‐component polyurethane (2K PU) clearcoats are widely used in automotive applications owing to their mechanical robustness, chemical resistance, and environmental stability. In original equipment manufacturing coating systems, hydroxyl‐functional polyols react with polyisocyanate crosslinkers to form dense urethane networks that impart hardness, abrasion resistance, and long‐term durability. In this study, hydroxyl‐terminated acrylic polyols are newly synthesized by copolymerizing acrylic monomers with ε ‐caprolactone‐based macromonomers of varying chain lengths. These tailored polyols are incorporated into 2K PU clearcoats to elucidate the structure–property relationships governing the crosslinking and mechanical performance. Thermal curing and network evolution were monitored using real‐time rheometry and in situ Fourier‐transform infrared spectroscopy. The thermal transition behavior, mechanical properties, and surface‐recovery performance of the cured clearcoats were evaluated using complementary thermal, mechanical, and surface characterization methods. Increasing the caprolactone chain length enhances the segmental mobility during curing, leading to more complete urethane conversion and a more homogeneous network structure. Consequently, the coatings exhibit improved energy dissipation, scratch recovery, and color stability after accelerated weathering. Overall, the caprolactone‐modified acrylic polyols provide an effective design strategy for developing self‐healing 2K PU clearcoats with balanced rigidity, flexibility, and durability for advanced automotive applications.