Photomodification of polymer films: azobenzene-containing polyurethanes

New results are presented on optical recording to the films of polymers substituted with azo dyes. Holographic gratings are formed in the polyurethane films by exposure to Ar(+) laser light without any post-treatment as in previous works using polyacrylates, epoxy-based polymers and polyesters substituted with azo dyes. It is shown for the first time that the principal mechanism of optical recording could be the mass transfer of polymers during the cis-trans isomerization of azo dye units on the polymers from illuminated areas to non-illuminated areas. Besides this transport, some irreversible photochemical reactions involving atmospheric oxygen are suggested as another possible origin for the holographic recording.