Testing of the ways for synthesis of new nonlinear optical epoxy-based polymers with azochromophores in the side chain

• New reactive oligomers with azochromophores in side chains are synthesized.
• One-stage method of the chromophore incorporation is shown to be favorable.
• NLO coefficients, d33, of the materials based on linear oligomers are ∼22 pm/V.
• The cross-linked materials have moderate temporal stability of d33.
• The values of d33 coefficients of cross-linked polymers are equal to 35.2 pm/V.

New polymer materials with quadratic nonlinear optical (NLO) response were synthesized on the basis of bisphenol A diglycidyl ether and p-aminobenzoic acid oligomers with azochromophores in side chains. The reactive polyether polyols were obtained either in solution, or in the bulk, the latter approach being found to be preferable as it provides obtaining oligomers with rather high molecular weight and high yield. The incorporation of chromophores into the oligomers side chain was carried out by etherification reaction using two synthetic approaches: in two steps, when an aniline-containing oligomer precursor is first obtained and then used in an azo-coupling reaction, giving the desired azochromophore-containing oligomer, or in one step via a direct attachment of a hydroxyl-containing azochromophore to the reactive oligomer. The advantage of the one-stage procedure is established, since the oligomer functionalization degree with chromophore groups reached 70 mol% in this case. The synthesized oligomers are characterized by high thermal stability and heat resistance; they demonstrate good film-forming ability. NLO coefficients, d33, of corona-poled films of the materials based on linear oligomers and cross-linked polymers amount to ∼22 and 35.2 pm/V, respectively. The cross-linked materials are shown to have moderate temporal stability of the second-order nonlinear optical characteristics.

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