Synthesis of stable cationic waterborne polyurethane with a high solid content: insight from simulation to experiment

Stable cationic waterborne polyurethanes (CWPUs) with a high solid content (HSC) were synthesized via the combination of cationic ionic and nonionic segments (polyoxyethylene alkyl amine, PAE). The process was based on an iterative strategy to design the cationic groups in soft segments and the chain terminal of polyurethanes (terminal ions) together with the determination of the optimal bimodal particle size distribution (PSD). The effects of the polymerization degree of poly(ethylene glycol) groups (PEG-g) in PAE and its interaction with the hydrophilic groups N-methyl diethanolamine (MDEA) in polyurethane were studied. It was found that the terminal ions resulted in a much finer dispersion, better dispersion stability, smaller particle size and lower viscosity. Moreover, the highest solid content (52.18%) of CWPU was obtained by the incorporation of PAE and a low terminal ions content of 2.5%, which had a bimodal particle size distribution. The increasing length of PEG-g was also found to enhance the thermal stability and render a better mechanical stability for the polyurethane films as the increasing PEG-g length may weaken the hydrogen bonding and reduce the extent of phase separation. The experimental results were further compared with molecular dynamic simulation results, which verified that the specific molecular structure of this WPU ensured its excellent properties. The static structure and dynamic properties obtained strongly supported the experimental observations reported on the morphology and thermal and mechanical properties of these polyurethanes.