2-Oxazoline based photo-responsive azo-polymers. Synthesis, characterization and isomerization kinetics

New azo-polymer structures, with azo content ranging from 15% to ≈100%, are prepared by attaching a side-chain azo-moiety onto poly(isopropenyloxazoline-co-styrene)s and poly(isopropenyloxazoline). Postcoupling conditions are determined by kinetic investigations. Polymer compositions are evaluated from UV, 1H NMR, titrimetry and elemental analysis. Chemical modification of polymers is evidenced by FTIR and 1H NMR spectroscopy. Thermal analysis sustain that azobenzene loads up to 0.67 M ratio result in an increase of Tgs, and that the azo dye content dictates the thermal stability of the modified copolymers. Both solution and solid-state trans–cis–trans isomerization kinetics are conducted. Cis-to-trans thermal relaxation rate constants of azo-polymers increase compared to the model compound used in solution measurements. Also, distinct relaxation mechanisms are assessed, as a function of solvents polarity and temperature for both polymers and model compound. For the azo-polymer thin films, the lifetime of cis isomers is tuned from polymer composition (dye load) to exhibit slow or fast relaxation.

Figure optionsDownload as PowerPoint slideHighlights
► A synthesis strategy is developed to yield balanced azo-polymer structures.
► A target substitution pattern is considered to retain the push–pull character of the dye.
► Implicit post-coupling conditions are determined by kinetic investigations.
► Isomerization behavior has been extensively studied in both solution and thin film.