Polyamide, azobenzene groups

Irie, M., and Schnabel, W. Photoresponsive Polymers On the Dynamics of Cainformaiioiial Changes of Polyamides with Backbone Azobenzene Groups. Macromolecules 14, 1246 (1981). 

Polyamides with azobenzene groups in the backbone are among the earliest in which trans-cis isomerizable chromophores were used to regulate the polymer conformation [13, 14]. The intrinsic viscosity [q] of polyamide (6) in polar AJV-dimethyl-acetamide was found to decrease from 1.22 to 0.5 dl/g upon ultraviolet irradiation... 

As an example of the first technique, let us consider the case of a polyamide containing photoresponsive azobenzene groups on its main chain (14). The distance between the two para-positions is 9.0 A in trans-azobenzene, and only 5.5 A in the cis-isomer. The cis-trans photoisomerization of these groups is reflected directly by a molecular expansion of the... 

In the case of an azobenzene-modified poly(arylether ketone amide) (see Chart 5.2), a pronounced volume contraction due to photo-induced trans-cis isomerization of the azobenzene groups was evidenced by means of size-exclusion chromatography (SEC) [25]. When irradiated in dilute N,JV-diethylacetamide solution, this polymer underwent a reduction in its hydrodynamic radius by a factor of 2.7, corresponding to a contraction of the hydrodynamic volume by a factor of about 20. This pronounced shrinkage effect is believed to be due to a large number of conformationally restricted backbone segments, because other more flexible polyamides and polyurea polymers exhibit much weaker contraction effects. 

Chart 5.3 Chemical structure of a polyamide containing in-chain azobenzene groups. Compact Conformation... 

Irie et al. [217] synthesized a number of polyamides with azobenzene groups in the backbone. All the polymers exhibit photo-viscosity effects. In solutimis in VA/ -dimethylacetamide, a 60% reduction in specific viscosity can be achieved by UV hght irradiation (410 > A > 350 nm). The initial viscosity is regained by storage in the dark at room temperature for 30 h. 

Polyamides, bearing azobenzene groups on the main chains, have been from the first macromoleculare supports used destinated to investigate the conformational changes occurring by UV irradiation [93, 94] ... 

Irie, M. and Schnabel, W. (1981) Photoresponsive polymers - on the dynamics of conformational-changes of polyamides with backbone azobenzene groups. Macromolecules, 14, 1246-1249. 

TABLE IV. Conformational relaxation of polyamide chains subsequent to cis trans isomerization of azobenzene groups in the backbone. 

It is interesting to note that the halflives of coil contraction of the copolymers decrease with the decrease in the azobenzene content and the values are slightly smaller than the halflives of coil expansion measured for polyamide having azobenzene groups in the main chain. 

Concerning the polymers, Irie and collaborators prepared a number of polyamides with azobenzene groups in the backbone (e.g., 21). The viscosity of the polyamides in a polar solvent decreased upon irradiation and returned to the initial value in the dark. 

---