Synthesis of Polymers Bearing Oligo‐Aromatic Esters for Second‐Order Nonlinear Optics

We synthesized methacrylate‐type polymers bearing oligo‐aromatic esters as side chains to create unique second‐order nonlinear optical (NLO) active polymers ( PMA n ‐x , PMA n C‐x , PMA2N‐x , and PBA3N‐x , x = oligo‐aromatic ester contents) for the investigation of the resulting architecture. The polymers were obtained from the polymerization of methacrylated oligo‐aromatic esters and the copolymerization of the esters with methyl methacrylate or tert‐butyl methacrylate using a radical initiator. The cut‐off wavelength (λ_co) of these polymers was shorter than the visible region aimed at, i. e. λ_co = ca. 330–370 nm, which is much shorter than λ_co of the typical second‐order NLO polymers containing groups such as azobenzene chromophores. Second‐harmonic generation (SHG) measurements of these polymer films after treatment by corona poling were carried out using the Maker‐fringe method. These polymer films exhibited good transparency in the visible region and a second‐order nonlinear optical coefficient d₃₃ of 2.2–9.8 pm·V^–1. The d₃₃ values of some derivatives decreased with an increase of the chromophore content, which is due to a strong interaction between the side chains with increasing chromophore content.