Synthesis and nonlinear optical properties of branched copolymers with covalently attached azochromophores

Soluble branched chromophore-containing nonlinear optical (NLO) methacrylate copolymers were synthesized by two-stage procedure. At the first stage aniline-containing precursors were synthesized by radical copolymerization of MMA with N-methyl,N-phenylamino-2-hydroxypropyl methacrylate (AMA) in various ratios (90:10; 80:20; 70:30) with ethylene glycol dimethacrylate, EGDMA, being used as branching agent and 1-decanethiol, DT, as a chain-transfer agent. At the second stage these precursors were functionalized by 4-nitrobenzene-diazonium tetrafluoroborate giving the azofunctionalized methacrylate units, MAZ; and copolymers with NLO groups in the side chains were obtained. The synthesized copolymers were studied and some physical-chemical characteristics were determined. On the base of the synthesized copolymers thin films were spin-cast, their thickness being measured by AFM technique. The polymer films were corona-poled and the NLO characteristics were determined by second harmonic generation technique. The values of d(33) are shown to depend noticeably on the chromophores concentration in the polymer; for various ratios of MMA:MAZ units (90:10; 80:20; 70:30) they are equal to 77 pm/V, 45 pm/V and 28 pm/V, respectively. The values of NLO coefficients of branched chromophore-containing polymers are essentially higher than those of linear analogues obtained earlier in spite of an essentially lower concentration of chromophore groups. (C) 2013 Elsevier Ltd. All rights reserved.