Selected Polymers that Contain Aromatic Ester Units: Synthesis, Photoreactions, and Refractive Index Modulation

Abstract Photoreactive polymers bearing aliphatic and aromatic esters of 4-(N,N-diphenylamino)phenol in the side chain, poly[4-(N,N-diphenylamino)phenyl acrylate] (P1) and poly[4-(N,N-diphenylamino)phenyl 4-vinylbenzoate] (P2), are prepared from their monomers by free radical polymerization. In addition, poly[naphthalene-1-yl 4-vinylbenzoate] is synthesized (P3). These materials absorb UV light up to λ = 350 nm. The polymers P1–P3 as well as low-molecular-weight model compounds are investigated with respect to their photoreactions under UV illumination. It is found that decarboxylation is the dominant reaction and that the photo-Fries rearrangement occurs as a minor reaction. The fully aromatic ester units in P2 are more reactive than the ester units in P1. In the polymers, decarboxylation proceeds more efficiently than in the low-molecular-weight model compounds. Upon UV illumination of the polymers, large increases of the refractive index are observed (Δn450 up to +0.07). This is in agreement with the structural changes in the polymers after irradiation as calculated from group contributions to molar refraction. A preliminary investigation under 610 nm fs laser irradiation indicates that refractive index patterns can be produced by two-photon effects (TPA). The polymers are of potential interest for applications in the field of optical waveguides.