Synthesis and Nonlinear Optical Properties of Polymers Containing Aromatic Ester Oligomers as Chained Chromophores

We synthesized some aromatic ester oligomers consisting of repeating units of oxy-1,4-phenylenecarbonyl group (ArESn, n=2∼4) as novel nonlinear optical (NLO) active chromophores and their methacrylate derivatives (ArESn-MA, n=2∼3). Some second-order NLO properties for poled polymer films of poly(methyl methacrylate) doped with 10 or 5wt% ArESn (ArESn/PMMA) and ArESn-MA homopolymers (poly(ArESn-MA)) as well as copolymers with MMA (poly(ArESn-MA-co-MMA)) were estimated by the second harmonic generation (SHG) measurement using Nd-YAG laser as light source. Comparison of the d 33 value at the chromophore molar concentration (d 33 (M)) for ArESn/PMMA films indicated that the d 33 (M) value of ArESn increases with increase in n and ArESn with n more than 3 reveal higher d 33 (M) value than that of pNA, in addition, every ArESn has cutoff wavelength (λ co ) of about 300nm, which is much snorter than the case of pNA (λ co =ca. 450nm). Moreover, poly(ArESn-MA) films exhibited much larger d 33 values than those of ArESn/PMMA films since the formers contain the chromophores in high concentration, however, when the comparison is made by using the d 33 (M) value the values become less than 1/2 of those in the cases of ArESn/PMMA films. This might be caused by a strong interaction acting among the chromophore side chains. Copolymerization of ArESn-MA with MMA which is capable of relieving the interaction improved the chromophore orientation considerably.