Azopolymers storage

Zucolotto V, Mendonca CR, dos Santos DS Jr, Balogh DT, Zilio SC, Oliveira ON Jr, Constantino CJL, Aroca RF. 2002. The influence of electrostatic and H bonding interactions on the optical storage of layer by layer films of an azopolymer. Polymer 43 4645 4650. 

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. 

Synthetic strategies to azopolymers for optical data storage... 

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). 

Forcdn, E, Oriol,L.,Sanchez, C., Rodriguez,F. J., Alcala, R., Hvilsted, S. and Jankova, K. (2007b) Methacrylic azopolymers for holographic storage A comparison among different polymer types , Eur. Polym. 43,3292-3300. 

---