Azo-containing polymers

The bifunctional azo initiator can initiate a polymerization of a monomer A forming a polymeric compound containing at least one azo group in its main chain [Figure 1, Scheme (1)]. Naturally, the monomer A has to have suitable sites for reacting with the transformation site F. The azo-containing polymers obtained in Scheme... 

The incorporation of thermally labile azo groups into polymer backbones was first reported in the early 1950s [2]. Since then, numerous techniques for synthesizing azo-containing polymers have been developed. The effort to create new azo-containing polymeric materials has been reviewed by several authors [3-8]. 

Low-molecular weight azo compounds have frequently been used in cationic polymerizations producing azo-containing polymers. Thus, the combination of ionically and radically polymerizable monomers into block copolymers has been achieved. Azo compounds were used in all steps of cationic polymerization without any loss of azo function as initiators, as monomers and, finally, as terminating agents. 

Where the azo groups form part of the polymer backbone their decomposition leads to a simultaneous fragmentation of the polymer. In the presence of a suitable monomer the radical terminated polymer fragments can initiate a polymerization and become part of a block copolymer. Thermolysis of azo functions which form part of the terminal moiety of a polymer also lead to block copolymers, but in this case no fragmentation of the azo-containing polymer occurs. 

The following reaction schemes show the principle of the grafting reactions using azo-containing polymers, whereby the azo groups are used as initiatiors of the graft monomers. 

Natanson A, Rochon P. (2002) Photoinduced motions in azo-containing polymers. Chem Rev 102 4139 175... 

The azoperester, t-butyl 4-methyl-4-(t-butylazo)peroxypentanoate, cleaves at the azo group on excitation to yield the y-perester radical (231). Cyclisation of (231) by attack on the peroxy linkage to yield the corresponding y-lactone occurs sufficiently slowly (1.5 x 10 s at 22 °C) that the azoperester precursor may be used as a photochemical bifunctional initiator. In contrast thermolysis occurs at the peroxy linkage. Decarboxylation and cyclisation of y-azo radical (230) occur so rapidly that an azo-containing polymer would not be produced.Diarylfur-oxans (232) yield 1,2-diarylacetylenes in low yield on irradiation. ... 

Natansohn, A., Rochon, P. (submitted). Photoinduccd morions in azo-containing polymers. Chem. Rev. 

Nakano, H. Tanino, T. Shirota, Y. (2005). Surface Relief Grating Formation on a Single Crystal of 4-Dimethylattiinoazoberizene. Appl. Phys. Lett., 2005,87, 061910/1-3. Natansohn, A. Rochon, P. (2002). Photoinduced Motions in Azo-Containing Polymers. Chem. Reo., 2002,102,4139-4175. 

Consequent upon these systems into materials may show effects on various chemical, mechanical, electronic and optical properties of the materials and can be used as photoswitches. An exhaustive research work has been carried out by various group of researchers onto the photoinduced motions in azo-containing polymers and liquid crystals as light-responsive materials [120-124]. 

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