Infra-red spectroscopy has been used to follow the evolution of the photopolymerization of mesogenic diacrylates in a liquid crystal matrix. The kinetic is a first order one as in isotropic solvents. The rate constant and the final conversion ratio depend on the monomer concentration. The order parameter of the liquid crystal decreases during polymerization due to reorganization. The electro-optical characteristics of a gel depend on the nature of the monomer and on the density of cross-linked bonds. A reversible electro-optical behaviour is observed with a high density of cross-linked bonds. Gels with low densities of cross-linked bonds exhibit a memory effect.