Strong-Interaction-Assisted Surface Fluorine Enrichment in Fluorinated AB-type Polyurethane Coatings

Achieving efficient hydrophobization in polyurethane coatings under low-fluorine modification remains challenging because surface functionality must be introduced without compromising bulk cohesion and mechanical integrity. Here, a fluorinated AB-type polyurethane (PUAB) was designed by combining thermally triggered self-polymerization with postpolymerization thiol–ene fluorination. The resulting PUAB matrix is stabilized by hierarchical hydrogen bonding and π-related interactions, while the limited compatibility and low surface energy of the fluorinated side chains promote their segregation toward the air-exposed surface during film formation. This bulk-interaction-assisted fluorine enrichment generated a fluorine-rich outer layer with submicron protrusions, enabling efficient surface hydrophobization at low fluorine content. Spectroscopic, thermal, microscopic, and computational analyses revealed the relationship between polymer backbone interactions and surface organization. The fluorinated PUAB coatings exhibited enhanced hydrophobicity, robust mechanical properties, good adhesion, and improved electrochemical barrier performance. This work provides a material design strategy for constructing low-fluorine polyurethane coatings through the coupling of strong bulk interactions and surface fluorine enrichment.