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

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.