Synthesis of azobenzene-functionalized two-arm, three-arm and four-arm telomers using polyfunctional chain transfer agents

BACKGROUND: Star-shaped polymers are very attractive because of their interesting properties such as reduced viscosity, good solubility, low glass transition temperature and fast response to external stimuli. The incorporation of azobenzene moieties in star-shaped polymers could significantly widen their potential applications in various optical devices. One of the most important properties of the azobenzene chromophore is its reversible trans-cis photoisomerization induced by UV or visible light. Photoisomerization induces conformational changes in azopolymer chains, which in turn lead to macroscopic variations in chemical and physical properties of the surroundings and media. RESULTS: This study reports the synthesis of azolbenzene-functionalized two-, three- and four-arm telomers via free radical telomerization using the di-, tri- and tetrafunctional chain transfer agents 1,2- and 1,4-benzenedimethanethiol, trimethylolpropane-tris(2-mercaptoacetate) and pentaerythritol-tetrakis(3-mercaptopropionate), respectively, in the presence of azobisisobutyronitrile. Azotelomers were characterized using gel permeation chromatography and H-1 NMR and Fourier transform infrared spectroscopy. Thermal phase transition behaviors were investigated using differential scanning calorimetry and polarized optical microscopy. Azotelomers synthesized in this study showed reversible photoisomerization and a fast generation of birefringence. CONCLUSION: Considering the photoisomerization behavior and birefringence of the two-, three- and four-arm azotelomers, it can be concluded that they could be potential candidates for use in various optical devices. (C) 2009 Society of Chemical Industry