Polymers containing azobenzene units are of special interest due to the reversibility of their photo‐orientation. Applications of these materials are in the fields of optical information storage, information processing, optical switching devices and others. In the work reported, we synthesized, characterized and compared the optical behaviour of azo‐modified epoxy polymers. With this goal in mind, Disperse Red 13 was selected as azo chromophore and two different amines, N,N‐benzyldimethylamine and 4‐(dimethylamine)pyridine, as initiators of the epoxy homopolymerization. The influence of the degree of union between azo chromophore and matrix in crosslinked polymers, and, in consequence, the azo mobility, on the optical behaviour (birefringence and dichroism) of resulting films was evaluated. An analysis of the dynamics of the writing and relaxation processes was also carried out. When the azo chromophore was covalently linked to the network, the maximum birefringence was reached three times faster. Also, two completely different optical behaviours were observed taking into account the occurrence or not of covalent bonding between the chromophore and the matrix. A remnant birefringence of around 60% was retained in the first case; an on‐off optical behaviour was observed in the second case. Copyright © 2011 Society of Chemical Industry The influence of the degree of union between azo chromophore and matrix in crosslinked polymer films on the optical behaviour (birefringence and dichroism) was investigated, and the dynamics of the writing and relaxation processes were analysed.