Azobenzenes copolymers

Figure 1. The UV absorption of a film of methylmethacrylate/4-methacrylamino-azobenzene-copolymer after different periods of irradiation (X = 355 nm) (3).

Willner I, Rubin S, Zor T. 1991b. Photoregulation of alpha chymotrypsin by its immobi lization in a photochromic azobenzene copolymer. J Am Chem Soc 113(10) 4013 4014. 

Saishoji, A., Sato, D., Shishido, A. Ikeda, T. (2007). Formation of Bragg Gratings with Large Angular Multiplicity by Means of the Photoinduced Reorientation of Azobenzene Copolymers. Langmuir, 2007,23,320-326. 

Feng,N.,Han,G.,Dong,J.,Wu,H.,Zheng,Y,Wang,G. (2014).Nanoparticle assembly of a photo- and pH-responsive random azobenzene copolymer, J. Colloid. Interfaces Sci., 421,15-21. 

Weener et al. prepared photo-responsive monolayers from azobenzene modified polypropylene imine) dendrimers which also hold promise in the area of optical data storage [74], A fifth generation polypropylene imine) dendrimer was functionalized with equal amounts of palmitoyl and azobenzene containing alkyl chains, resulting in the formation of an amphiphilic copolymer with a random shell structure (Figure 16.5). 

The photoisomerization of several copolymers was studied, in order to determine the effects of the structure and switching of the chiral side chain on the helicity of the main chain. A delicate balance of parameters was found, including separation and nature of the stereocenters, solvent, and concentration of azobenzene moieties J77 Stereoselectivity was often greatly enhanced if the chiral moieties were closer to each other. Accordingly, it was found that the incorporation of the stereocenter into a short, two-carbon spacer resulted in much more pronounced helical preference, as well as CD effects at lower chiral chromophore concentrations. The greater helical twist and improved thermal stability of the cis form (half-life 40h at RT) are notable features. 771 It was also found that the relationship between the trans-cis... 

More recently, Ueno et al. have prepared and investigated a new series of copolymers containing p-phenylazobenzyl-L-aspartate and n-octadecyl-L-aspartate residues (Scheme 7, Structure XII). 55 561 In the case of copolymers containing less than 50 mol% azo residues, the CD spectra at 25 °C were consistent with the presence of right-handed helical conformations, which were not affected by irradiation at 320 nm. In contrast, in the case of copolymers containing 68 and 89 mol% azobenzene groups, irradiation caused the reversal of helix sense from the left-handed to the right-handed form. 

Oge and Zentel [119] have studied a ferroelectric SCLC copolymer, 53, containing a photoisomerizable, chiral 4,4 -bisalkoxyazobenzene mesogen together with a chiral 4-alkoxyphenyl-4 -alkoxybenzoate mesogen that is photo-chemically unreactive at wavelengths where the azobenzene moiety can be photo-excited. This polymer has both a ferroelectric Sc. phase and a SA phase. Films... 

The H and 13C NMR spectra of azo compounds incorporated into monomers and polymers have been measured.67-73 Chiral methacrylic polymers containing azobenzene chromophore,67,68 epoxy-based polymers functionalized with tricyanivinylphenylazo chromophores,69 4-vinylazobenzene and homo- and copolymers,70 microstructure of trans-4-acrylooyloxyazo-benzene/methyl methacrylate copolymers,71 optically active poly[(S)-4-(2-methacryloyloxypropanoyloxy)azobenzene]72 and polyetherurethane pendant with azo dye by TV-substitution73 have been studied. 

Triphenylmethyl methacrylate (TrMA) and azobenzene-modified methacrylates were randomly copolymerized in toluene at — 78°C with chiral catalysts to give optically active helical copolymers (19 in Fig. 6) [65]. The optical activity (optical rotation) of the copolymers decreased with the increasing content of the azobenzene-modified methacrylates in the copolymers. The single helical conformation of PTrMA is quite stable in solution, but the copolymers of TrMA with less bulky methacrylates cannot keep their helical structure and lose their optical activity during the polymerization or after the polymerization in solution, which is highly dependent on the bulkiness of the comonomers [22]. The copolymer (19 x = 2) containing 26 mol% azobenzene units, also lost its optical activity upon irradiation within 20 min. This change is due to the helix-to-coil transition of the copolymer and can occur in the dark. 

Figure 13 shows several optically active vinyl polymers and copolymers with azobenzene or stilbene residues in the side groups. All these polymers were prepared by the conventional radical polymerization, so that the main chains should be atactic or syndiotactic and may not be able to take a helical conformation even in the presence of chiral pendants. The homopolymers (28-31) [83-85]... 

Su W, Han K, Luo Y et al. (2007) Pormation and photoresponsive properties of giant microvesicles assembled from azobenzene-containing amphiphilic diblock copolymers. Mac-romol Chem Phys 208 955-963... 

Tong X, Wang G, Soldera A, Zhao Y. (2005) How can azobenzene block copolymer vesicles be dissociated and reformed by light J Phys Chem B 109 20281-20287... 

Wang G, Tong X, Zhao Y. (2004) Preparation of azobenzene-containing amphiphilic diblock copolymers for light-responsive miceUar aggregates. Macromolecules 37 8911-8917... 

Tong X, Cui L, Zhao Y. (2004) Confinement effects on photoahgnment, photochemical phase transition and thermochromic behavior of liquid crystahine azobenzene-containing diblock copolymers. Macromolecules 37 3101-3112... 

Scheme 12 Top LC copolymers containing mesogenic side groups and carboxylic side groups capable of hydrogen bonding. Bottom Azobenzene-containing dopants with pyridine ring and with a primary amine group ensuring the formation of donor-acceptor hydrogen bonds. Reprinted from [23,252]. 2003, with permission from Elsevier...

More recently, a similar photocfaromic behavior was observed by Eisenbadi for the cis-trans isomeriration of azobenzene residues attached as side groups to copolymers when examined below their ass transition temperature. These copolymers were obtained by copolymerization of the mtmomers 4-methacryloylaminoazobenzene (TV) and 4-(3-methacryloyloxybutylcarbonylamino)azobenzene (V) with various alkyl acrylates and methacrylates. 

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