Hyperbranched Azo-Polymers Synthesized by Azo-Coupling Reaction of an AB₂ Monomer and Postpolymerization Modification

Abstract

A series of hyperbranched azo-polymers have been synthesized by two-stage azo-coupling reactions, in which a hyperbranched precursor azo-polymer (HPAP) was prepared by step-growth polymerization of an AB 2 monomer through azo-coupling reaction and then was further modified by postpolymerization azo-coupling reaction at the peripheral groups. The AB 2 monomer, di[2-( N -ethylanilino)ethyl]-5-aminoisophthalate, was synthesized from the nucleophilic substitution reaction between N -ethyl- N -(2-chloroethyl)aniline and 3,5-bis(carboxyl)aniline. On the basis of the monomer, HPAP was prepared by step-growth polycondensation of the diazonium salt of the AB 2 monomer. The hyperbranched precursor polymer was then reacted with diazonium salts of 4-nitroaniline, 4-aminobenzoic acid, and 4-aminobenzonitrile to introduce different types of donor−acceptor azo-chromophores at the peripheral positions. The structure and properties of the azo-polymers were characterized by the spectroscopic methods and thermal analysis. The hyperbranched azo-polymers were used to fabricate surface relief gratings (SRGs) by exposing spin-coated thin films of the polymers to an interference pattern of Ar + laser beams at modest intensity (150 mW/cm 2 ). The type of electron-withdrawing groups in the para-positions of the terminal azobenzene units shows a significant effect on the SRG inscription rate. The synthetic scheme demonstrated in this work is a feasible way to prepare a variety of hyperbranched azo-polymers under extremely mild conditions. The hyperbranched azo-polymers can potentially be used for applications such as reversible optical data storage, photoswitching, sensors, and other photodriven devices.