Aqueous dispersions of polyurethane cationomers: a new approach for hydrophobic modification and crosslinking

Polyurethanes (PUs) containing tertiary nitrogen atoms were synthesised from poly (tetramethylene oxide) glycol, toluene diisocyanate and N-methyl diethanolamine. These polymers were converted into cationomers by quarternising with alkyl bromides of different chain lengths and then dispersed in water. Finally the cationic PU dispersions were further crosslinked with dibromo compounds of different spacer lengths. The effect of percent ionisation, percent crosslinking, chain length of the ioniser and crosslinker on particle size, viscosity and interfacial tension of the dispersions and on the thermal, mechanical and surface tension properties of the dispersion cast films were studied. The hydrophilicity of the polymer is more in the dispersed state than when cast as a film, which exhibited low critical surface tension values. With increase in chain length of the ioniser and the crosslinker, the hydrophobicity of the dispersion cast film increases without appreciable change in the hydrophilicity of the polymer in the dispersed phase, as can be seen from the interfacial tension and critical surface tension values.