Synthesis and photochromic behavior of new polyimides containing azobenzene side groups

Aromatic polyimides containing side azobenzene groups have been synthesized by low-temperature solution polycondensation of certain aromatic dianhydrides with aromatic diamines containing preformed side azobenzene groups followed by chemical imidization at 100 °C in the presence of pyridine and acetic anhydride. The weight average molecular weight of these polymers is in the range of 16,000–129,000. The glass transition temperature of these polyimides is in the range of 185–230 °C. The polymer architecture presents a special characteristic, one of the azobenzene aromatic units being in the main chain of the polymer. This situation is intermediary between main-chain and side-chain azobenzene-containing polymers. The photochromic behavior, determined by the trans–cis isomerization process of azo-groups, in solution and in solid state, was evaluated. The synthesized polyimides were studied by spectral methods (UV, IR), thermal analysis and molecular modeling. A preliminary study concerning the surface structuration capacity of the polyimides was accomplished. Good results were obtained using Nd:YAG laser at 355 nm, at an incident fluence of 35 mJ/cm2 (situated below the laser ablation limit).