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BACKROUND: One of the most important properties of the azobenzene chromophores is the photochemical trans-cis isomerization induced by UV or visible light. In azopolymers, the photoisomerization induces conformational changes in the polymer chains, which in turn lead to macroscopic variations in the chemical and physical properties of the surroundings and media.RESULTS: This work reports the photochromic behaviour and surface structuring capacity of azopolymers having rigid polyimide and flexible polysiloxane structures, respectively. These polymers have good thermostabilities, with the degradation process starting above 315 • C. The glass transition temperature of the azopolyimide is 228 • C, while that of the azopolysiloxane modified with thymine is 34 • C. CONCLUSION:The experiments show that the azobenzene groups can isomerize even in the case of the rigid polyimide, but the maximum degree of conversion to the cis isomer is less than in the case of the flexible polysiloxane. This behaviour is reversed in solution, probably due to both the thymine and azo group interactions and for conformational reasons. The azopolymers show a good surface structuring capacity. The polysiloxane is more sensitive in the case of low irradiation energy and irradiation time. By increasing the irradiation time for both polymers, the modulation depth increases and has comparable values.

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Polymers capable of generating surface relief gratings (SRGs) were studied intensively in the last period for their applications in hot research areas, such as data storage, solar energy conversion, plasmonics, and biology. In the case of azopolymers, SRGs can be generated by two main procedures: pulsed or continuous laser irradiation. In this article, we discuss the possibility of obtaining stable SRGs with azopolysiloxanes with low glass‐transition temperature values, depending on the illumination type. These studies evidenced that the polymer chemical structure had a strong influence on the SRG stability in time. For the unsubstituted azobenzene, unstable surfaces resulted, whereas for the substituted azo groups stable reliefs were obtained. A parallel discussion between the pulsed and continuous irradiation techniques and structuration mechanisms is given. The operational conditions strongly affected the relief quality when the pulsed laser irradiation method was used. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41015.

Azobenzene polymers have been the subject of intensive research due to their unique and unexpected properties that allow various applications triggered by light. One of their attractive features is the possibility of changing the orientation of azobenzene chain through trans-cis-trans photoisomerization cycles to photoinduce birefringerence and linear dichroism in thin polymer films. The photochromic behavior and surface structuring capacity of rigid or flexible polymers having side azobenzene units have been investigated. The polyimides with side azobenzene units have rigid structure, while polysiloxane chains modified with azobenzene groups and nucleobases are considered materials with flexible structure. During the photochromic studies of the investigated polymers, a mechanism concerning the possibility to generate a fluid phase under UV/VIS irradiation was proposed. The photoisomerisation kinetic by UV-Vis irradiation in the solid state compared with the solution and the cis-trans azobenzene relaxation phenomena were presented. The surface structuring capacity of these polymers was studied using a Nd:YAG laser at 355 nm, at different incident fluencies and pulse numbers.