FABRICATION OF PHOTORESPONSIVE ELECTROSTATIC MULTILAYERS CONTAINING DIAZONIUM-HYPERBRANCHED AZO POLYMER

Abstract

A novel hyperbranced azo polymer with terminal diazonium groups was synthesized by step-growth polymerization of 4,4'-diamino diphenyl sulphone's diazonium salts(A_2)and benzene-1,3,5-tricarboxylic acid tri-2-(N-ethylanilino)ethyl ester(B_3)through azo-coupling reaction.4,4'-diamino diphenyl sulphone(0.248 g,1 mmol)was dissolved in a hot homogeneous mixture of glacial acetic acid(7.5 mL)and sulfuric acid(1 mL).Aqueous solution of sodium nitrite(0.166 g,2.4 mmol)in 0.5 mL water was added dropwise into the solution at 0℃ and kept at this temperature for 5 min.The diazonium salt solution of 4,4'-diamino diphenyl sulphone was then added dropwise into the solution of benzene-1,3,5-tricarboxylic acid tri-2-(N-ethylanilino)ethyl ester(0.326 g,0.5 mmol)in 50 mL DMF at 0℃.After the reaction was carried out at 0℃ for 8 h,the solution containing the diazonium-hyperbranched azo polymer was directly used as the polycation solution.The purchased sodium polystrene sulfonate(PSSA)was used as polyanion.Then the multilayer films were prepared by an electrostatic layer-by-layer deposition method.The self-assembly processes and morphologies of surfaces were characterized by UV-Vis spectra,ellipsometer and AFM.A linear increase of absorbance and thickness was observed as the number of the bilayers increased.Dichroism was optically induced in the self-assembly film under the irradiation of a polarized Ar+ laser beam at 488 nm.After 15 min irradiation of the laser beam at an intensity of 80 mW/cm2,the orientation order parameter of the multilayer film obtained was about 0.02.With interfering illumination of Ar+ laser beams for 30 min,significant surface relief gratings formed on the self-assembly multilayer film were observed.The spatial period and height of the obtained SRGs were about 744 nm and 20 nm,respectively.