Bonding and molecular environment effects on photoorientation in epoxy-based polymers having azobenzene units

An azo prepolymer (TAZ) was synthesized by reaction between Disperse Orange 3 (DO3) and diglycidyl ether of bisphenol A (DGEBA). The resulting TAZ was blended with DGEBA and two different monoamines, one aliphatic and one aromatic, benzylamine (BA) and m-toluidine (MT), to prepare various azo copolymers with different azo contents. In addition, two guest-host systems were prepared: 5.16% by weight of DO3 in DGEBA-BA and in DGEBA-MT polymers. Their reversible optical storage properties were studied and compared. The maximum obtainable birefringence increases linearly with TAZ weight fraction, independently of the power of the writing beam, the environment in which the azo moiety is located, and the bonding between the dye and the matrix. It was found that, in BA-based copolymers, with lower T_g, the fraction of birefringence conserved after relaxation is smaller and the writing rates are higher than in MT-based copolymers. The film thickness dependence of the birefringence signal is also analyzed.