Synthesis and characterization of some polyurethane cationomers with photochromic azoaromatic groups

Polyurethane cationomers based on polytetramethylene oxide, 4,4′-dibenzyldiisocyanate and N,N′-bis(β-hydroxyethyl)piperazine quaternized with methyl iodide were prepared. Using an ionic exchange reaction between this polycation and 3(p-oxyazobenzene)-propanesulfonic acid sodium salt, two azo-cationomers bearing chromophoric groups as counterions of ammonium quaternary structure were reported. The photochromic behavior of the above mentioned polycations in polymer solution as well as in thin films exposed to UV irradiation was discussed by comparison with other polycations having an azo dye (methyl orange) in the same hard segment. The increase of azo photochromic group concentration into polymer chains leads to a decrease in the isomerization rate.