Self‐Assembly Behavior and Mechanism of Anionic Amphiphilic Polyurethane in Water/Acetone Medium: Effects of Molecular Structure and Acetone Content

ABSTRACT To prepare stable, high solid content or low viscosity waterborne polyurethane (PU) dispersion from PU with a low hydrophilic group content is still challenging. In the present work, anionic amphiphilic PU prepolymer with different chemical and sequential structures was synthesized, dissolved in acetone and then self‐assembled in water. Effects of PU prepolymer structure and the composition of the dispersion phase on the self‐assembly behavior and mechanism were elucidated by low‐field nuclear magnetic resonance, particle size distribution and surface tension analysis, and molecular dynamics simulations. It demonstrates that the hydration of hydrophilic groups and the association of hydrophobic segments serve as the primary thermodynamic driving forces for the self‐assembly of amphiphilic PU prepolymer, and the concentration of PU prepolymer‐acetone solution alters the nucleation mechanism of the assembly. A dual‐hydrophobic‐chain structure significantly enhances hydrophobic association through a multipoint bridging effect. Consequently, the resulting waterborne PU dispersion exhibited a smaller particle size (average ≈90 nm) and a greater utilization efficiency of hydrophilic groups. A suitable acetone content in the PU prepolymer solution (< 55 wt%) facilitates preparation of waterborne PU dispersion with a high colloid stability.