Polymerization azopolymers

Polymerization of Primary Aromatic Diamines to Azopolymers by Oxidative Coupling... 

In studying this novel oxidative polymerization we investigated the following points in particular (a) scope of the reaction, (b) side reactions, (c) catalysis, (d) molecular weights obtainable, (e) properties of aromatic azopolymers in bulk and fabricated form. 

The monomers were then thermally polymerized and simultaneously irradiated with linearly polarized light. Two of the monomers were able to induce bulk alignment of the liquid crystals in direction perpendicular to the polarized light. Monomer 1 was effective in concentrations as low as 1%. It was also concluded from the experimental evidence that the photo-induced bulk alignment of the ferroelectric liquid crystals may take place by a mechanism that is different from one that takes place in achiral azopolymers. 

Zhang, Z., Wang, Y, Yan, R, Peng, D., Ma, Z. (2011). Photosensitive azopolymer brushes via atom transfer radical polymerization for protein sensing. Chinese Journal of Chemistry, 29, 153-158. http //dx.doi.Org/10.1002/cjoc.201190044. 

Abstract Smart polymers based on photoresponsive azobenzene moieties have been extensively explored as potential materials for high capacity optical storage. This chapter reviews different strategies to incorporate azobenzenes into polymeric structures as well as their photoresponse properties. The potential of this type of materials as volume holographic media is summarized with special emphasis on block copolymers and blends. Although side-chain azopolymers has been the most investigated, new macromolecular architectures have been recently proposed and will be briefly presented. 

These modifications include variations on the length of the spacer which connects the azobenzene and the polymeric chain in side-chain azopolymers, or the electronic nature of substituents at the azobenzene moiety (Ruhmann, 1997). This requires the synthesis of appropriate monomers. Conventional techniques can be used for the polymerization of azobenzene monomers. For instance, step polymerization has been used by Hvilsted and co-workers to synthesize different series of liquid crystalline polyesters with potential applications in reversible optical data storage. These polyesters have a side-chain architecture, which synthesis is represented in Fig. 16.6 (Hvilsted et al, 1995). Being a modular synthetic approach, the influence of different structural parameters on the photoinduced optical properties can be evaluated in relatively simple manner. 

The vast majority of azopolymers developed for optical storage are polyacrylates and polymethacrylates, which are generally prepared by free radical chain polymerization in solution using conventional experimental conditions. For example, azobisisobutyronitrile (AIBN) is used as a thermal initiator in dry organic solvents such as A(A-dimethylformamide (DMF), tetrahydrofuran (THF) or dioxane as the most common. Occasionally, the polymerization process of azobenzene (meth)acrylates can be limited by the radical transfer reaction promoted by the azo group, which seems to be associated with the formation of hydrazyl radicals (Nuyken and Weidner, 1986 Hallensleben andWeichart,1989). 

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