Photo- and pH-sensitive azo-containing cationic waterborne polyurethane

In this study, a novel photo- and pH-sensitive cationic waterborne polyurethane containing side chain aromatic azo groups (Azo-CWPU) was synthesized by step-growth addition polymerization from polyether polylol, isophorone diisocyanate, N-methyl diethanolamine and a new aromatic azo-containing monomer, 2,2'-(4-((4-ethylphenyl)diazenyl)phenylazanediyl)diethanol (EDPD). Azo-CWPU showed a significant hypsochromic contrast to the azo monomer and rapid changes in UV-Vis absorption spectra at different irradiation times. Azo-CWPU dispersion displays bright yellow, orange and red color with the change of pH values. Regarding the orange dispersion, we assume that there is a mixture of the azoic form and the hydrazone form. Compared to cationic waterborne polyurethane dispersion without aromatic azo groups (CWPU), Azo-CWPU dispersion with smaller hydrodynamics radius and more narrow distribution shows good thermodynamic properties of polyurethane.