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Azo-modified polymers

Figure 7.1. Structures of azo-modified polymers (here random copolymers) that have been used in solution to trigger phase separation, physical gelation, or photoswelling of chemical gels. n = 5-11 (Pouliquen and Tribet, 2006) RI =CH3 and R2 = H (Irie, 1993) or RI = H and R2 = H, methyl, ethyl, or butyl (Howley et al., 1997). Figure 7.1. Structures of azo-modified polymers (here random copolymers) that have been used in solution to trigger phase separation, physical gelation, or photoswelling of chemical gels. n = 5-11 (Pouliquen and Tribet, 2006) RI =CH3 and R2 = H (Irie, 1993) or RI = H and R2 = H, methyl, ethyl, or butyl (Howley et al., 1997).
Figure 7.6. Indices of association of azobenzene onto hydrophobic domains, (a) Representative spectra of an azo-modified polymer in water (under blue exposure) with increasing concentration of surfactant Cl 2E4 (0-0.4 g/L). Polymer structure cf. left-hand side in Fig. 7.1, with n = 11 andx = 2%. (b) Variation of the fraction of bound azobenzene upon addition of Triton X 100 in a solution of polymer at fixed concentration (polymer similar as in (a), with n = 5 and x = 4%). Figure 7.6. Indices of association of azobenzene onto hydrophobic domains, (a) Representative spectra of an azo-modified polymer in water (under blue exposure) with increasing concentration of surfactant Cl 2E4 (0-0.4 g/L). Polymer structure cf. left-hand side in Fig. 7.1, with n = 11 andx = 2%. (b) Variation of the fraction of bound azobenzene upon addition of Triton X 100 in a solution of polymer at fixed concentration (polymer similar as in (a), with n = 5 and x = 4%).
Figure 6 Variation of the viscosity as a constant polymer concentration, as a function of the colloid/azo-modified polymer ratio (o) BSA +7% 150-4.5azo, (U) CD-EP + 1% 150-4.5azo, ( ) BSA + I%l50-lcl8-4.5azo, (A) SDS + 2% 150-lcl8-0.5. (Shear rate lOs f. Figure 6 Variation of the viscosity as a constant polymer concentration, as a function of the colloid/azo-modified polymer ratio (o) BSA +7% 150-4.5azo, (U) CD-EP + 1% 150-4.5azo, ( ) BSA + I%l50-lcl8-4.5azo, (A) SDS + 2% 150-lcl8-0.5. (Shear rate lOs f.
The introduction of azobenzene units into the side chains of poly(L-lysine) has been achieved be means of various procedures and different azo reagents. The polymers described initially contained azobenzene units linked to the lysine side chains by means of an amide moiety 29-311 (Scheme 4, Structure V). More recently, Fissi et al. 321 have described azo-modified poly(L-lysine) in which the azobenzene units are linked to the Lys side chains by means of a sulfonamide function (Scheme 4, Structure VI). The two families of azo-modified poly(L-lysine) have been found to exhibit completely different conformational and photoresponsive behavior. [Pg.410]

Poly(L-lysine) containing azobenzene units linked to the side chains by means of a sulfonamide function (Scheme 4, Structure VI), was obtained by treating poly(L-lysine) with p-phenylazobenzenesulfonyl chloride. The poly(a-amino acid) was modified quantitatively conversion to the azo-lysine units of VI was effectively 100%. The azo-modified polypeptide was soluble in HFP, in which it exhibited an intense photochromism attributed to the trans-cis photoisomerization of the azobenzene units. Like other sulfonated azobenzene compounds, 33 azosulfonyl-modified polymers of L-lysine were found to be very stable in their tis form, and no thermal decay was observed at room temperature over periods of times as long as several weeks. Interconversion between the two forms at room temperature could only be effected by irradiation at appropriate wavelengths. This behavior allowed the authors to purify the trans and cis forms of the model compound NE-azobenzenesulfonyl-L-lysine (VII) by chromatography, and to measure the absorption spectra of the two pure photoisomers. [Pg.411]

Azo-benzene molecules are widely recognized as attractive candidates for many nonlinear optical applications. A highly deformable distribution of the ic-electron gives rise to very lar molecular optical nonlinearitics, Phdto-isomerization of azo molecules allows linear and nonlinear macroscopic susceptibilities to be easily modified, giving an opportunity to optically control the nonlinear susceptibilities. In this chapter, we will discuss third-order nonlinear optical effects related to photoisornerization of azo-dye polymer optical materials. [Pg.366]

FIG. 21 Photoresponse of the viscosity of a 1 wt% solution of an azo-modified HMPA in the presence of 0.6 wt% bovine serum albumin. Arrows correspond to the onset of UV irradiation alternatively at 365 nm (increase in the viscosity) or 436 nm (decrease). The polymer was grafted by 0.5 mol% of azobenzene and 1 mol% of C18 side groups. A factor of 20 between the high and low plateau-values was achieved in recent results by G. Pouliquen and C. Tribet. (Reprinted with permission from Ref. 95. Copyright 1999 American Chemical Society.)... [Pg.724]

Figure 7.2. Photoswitch of the solubility of chains, (a) Schematic drawing of the phototriggered coiiapse and aggregation of azobenzene-containing polymers in poor soivent conditions or ciose to iow critical solubility temperature (LCST). (b) Typical variation of the radius of the chains as a function of solvent parameter, or temperature in the case of chains having a LCST in water. Bold line parent chain with no azobenzene dashed and dot-dashed lines azo-modified chains, respectively, exposed to UV and dark-adapted. Figure 7.2. Photoswitch of the solubility of chains, (a) Schematic drawing of the phototriggered coiiapse and aggregation of azobenzene-containing polymers in poor soivent conditions or ciose to iow critical solubility temperature (LCST). (b) Typical variation of the radius of the chains as a function of solvent parameter, or temperature in the case of chains having a LCST in water. Bold line parent chain with no azobenzene dashed and dot-dashed lines azo-modified chains, respectively, exposed to UV and dark-adapted.
The formation of responsive clusters of macromolecular chains, or gels of interconnected chains is achieved using hydrophobically modified polymers in presence of various additives, such as micelles of surfactants, CDs or proteins which bind to the hydrophobic side groups of the polymers. Hydrophobically modified polymers show the strong vlscoslflcatlon and high sensitivity to external stimuli. The use of mixtures of azobenzene-modified polymers with CD polymers allows to achieve photoviscosity swings by ca a decade at submillimolar concentrations of azo dyes [71]. [Pg.835]

The first method in this application, however, was limited to modifying alcohol-containing colorants onto polymers containing grafted succinic anhydride transesterification, and transaminated reactions were also reported. In the second method water-soluble colorants were prepared by azo coupling of colorants with alkoxyether functionalized aniline. [Pg.4]

The azo (V-oxide (75) was reduced in DMF to the dianion of azopyridine.118 Electroinitiated polymerization of a 2-azopyridine gave a polymer useful for modifying electrode surfaces.119 The only other reports of azopyridine electrochemistry involve voltammetry.120... [Pg.192]

Fig. 3 Photoresponsive polymer surface sensitive to pH and light. Adsorption and release of cytochrome c triggered by pH (b, c, and d) release of the polymer layer and cytochrome c by breaking the host-guest interactions between surface-tethered azo dye and cyclodextrin via light irradiation (a and d). The molecular structure on the right represents the host-guest complexa-tion of the azo dye with the cyclodextrin-modified poly(acrylic acid). Reprinted, with permission, from [68]. Copyright (2009) Wiley Interscience... Fig. 3 Photoresponsive polymer surface sensitive to pH and light. Adsorption and release of cytochrome c triggered by pH (b, c, and d) release of the polymer layer and cytochrome c by breaking the host-guest interactions between surface-tethered azo dye and cyclodextrin via light irradiation (a and d). The molecular structure on the right represents the host-guest complexa-tion of the azo dye with the cyclodextrin-modified poly(acrylic acid). Reprinted, with permission, from [68]. Copyright (2009) Wiley Interscience...

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See also in sourсe #XX -- [ Pg.45 ]




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