Terminal Hydrophilicity-Induced Dispersion of Cationic Waterborne Polyurethane from CO2-Based Polyol

Cationic waterborne polyurethane (CWPU) was initially developed as a specific adhesive for anionic surface but now is ubiquitous in innovative material systems such as poly(ionic liquid)s, polyelectrolytes, antibacterial coatings, and drug carriers. However, state-of-the-art CWPU faces imperative challenges like easy degradation and poor water resistance, which is caused by excessive incorporation of internal emulsifiers with tertiary amines into the backbone than necessary, since emulsification performance of cationic internal emulsifier is much less efficient compared with the anionic analogue. Here, a terminal internal emulsifier-induced efficient dispersion strategy was developed. Taking oligo(carbonate ether) diol (a CO2-polyol from telomerization of CO2 and propylene oxide) as example, stable CWPU with only 1.00 wt % internal emulsifier was prepared. An emulsifying capacity parameter was introduced to quantitatively evaluate the emulsification performance of internal emulsifier according to its steric hindrance and mobility, and the terminal internal emulsifier was proven to show the highest emulsification performance. The terminal hydrophilicity-induced dispersion strategy exhibits excellent universality for a broad range of oligomer diols, effective not only for CO2-polyols but also for widely used polyether polyols and polyester polyols, affording CWPU with excellent water resistance. Therefore, the chemistry disclosed here paves a way for a vast number of water- and oxidation-resistant CWPUs which were hardly available until now.