Photochromic properties of polyimide and polysiloxane azopolymers

Abstract

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.

Photoinduced birefringence of novel azobenzene poly(esterimide)s; the effect of chromophore substituent and excitation conditions

“…The obtained values of thermal decomposition temperatures are similar to those obtained for other poly(esterimide)s containing either cyano and nitro substituent in para position[16]. Azopolymers containing covalently bonded chromophore usually are characterized by two or three degradation steps[26]. Such a behavior was also detected in the case of investigated poly(esterimide)s. The first decomposition step with maximum rate of the degradation temperature (Tmax) determined from the dynamic thermogravimetric (DTG) at 280-311 °C is probably connected with scissions of chromophore moieties[26].…”

“…Azopolymers containing covalently bonded chromophore usually are characterized by two or three degradation steps[26]. Such a behavior was also detected in the case of investigated poly(esterimide)s. The first decomposition step with maximum rate of the degradation temperature (Tmax) determined from the dynamic thermogravimetric (DTG) at 280-311 °C is probably connected with scissions of chromophore moieties[26]. The second one with Tmax in the range 338-383 o C is connected with a degradation of polymer backbone.…”

Poly(amic acid)s and their poly(amide imide) counterparts containing azobenzene moieties: Characterization, imidization kinetics and photochromic properties

“…In the case of the prepared PIs the temperature of the maximum decomposition rate, as evidenced by the dynamic thermogravimetric (DTG) curves, was in the range of 310e655 C. The first step of the T max appearing in the range of 310e378 C was probably connected with scissions of the chromophore moieties. The second step observed in the range of 594e655 C might be connected with degradation of the polymer main-chain [38]. The investigated azopolyimides exhibited a high residual weight at 800 C, which was in the range 44e60%.…”

“…They almost doubled or more than doubled the values found for the PI-1 polymer. Azopolymers containing covalently bonded chromophores are usually characterized by two degradation steps [38,39]. In the case of the prepared PIs the temperature of the maximum decomposition rate, as evidenced by the dynamic thermogravimetric (DTG) curves, was in the range of 310e655 C. The first step of the T max appearing in the range of 310e378 C was probably connected with scissions of the chromophore moieties.…”

Tridimensional Surface Relief Modulation of Polymeric Films

“…12.). AFM profiles of the surface relief induced under the action of an interference field with a medium fluence of 8.4 mJ/cm 2 and 100 subsequent laser pulses are similar for both azopolymers, with rigid and flexible main chain (Sava et al 2008). The depth of the induced structure is about 90 nm for the azo-polymer film and 100 -110 nm for the azoplyimide film (Fig.…”