In-Chain Core–Shell Dispersion for Enhanced Cross-Linking Networks in Waterborne Acrylic Polyurethane Coatings

초록

Waterborne polymer coatings are widely adopted due to their environmental advantages; however, their performance is fundamentally constrained by limited polymer chain interdiffusion during film formation. This kinetic restriction produces spatially heterogeneous cross-linking, thereby compromising network integrity and mechanical robustness. In this study, we report a core–shell dispersion in which hydroxyl and blocked isocyanate functionalities are covalently incorporated within a single polymer chain (In-chain). Unlike Ex-chain or encapsulated polyisocyanate systems, the In-chain spans both the core and shell domains of colloidal particles, ensuring a homogeneous distribution of complementary reactive groups. Thermal activation thus induces efficient intra- and interparticle cross-linking, even under conditions of restricted chain mobility. Various mechanical analyses revealed marked improvements in the storage modulus, glass transition temperature, surface hardness, and scratch resistance for the In-chain compared to reference dispersions. Molecular simulations corroborated these findings, demonstrating that the In-chain maintains molecular-level spatial proximity between hydroxyl and isocyanate groups, thereby facilitating cross-link density evolution independent of polymer interdiffusion. As a whole, these results establish that embedding mutually reactive functional groups within a single polymer chain provides an effective strategy to circumvent interdiffusion limitations, enabling waterborne coatings with mechanical and thermal performance approaching that of solventborne coatings.

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