Synthesis, thermal and solar cell application of novel hyperbranched polyurethanes containing azomethine and aryl-ether connectivities

Abstract

Bis-{[(4-hydroxybutoxyphenyl)methylidene]aminophenoxyhexyl}benzene-1,3-dicarboxylate – a novel A2 diol monomer – and a series of new blocked isocyanates (B3 monomers) were synthesized in high yield and their structures were confirmed. Using these monomers, different hyperbranched polyurethanes (HBPUs) containing azomethine and aryl-ether connectivities were prepared via an A2 + B3 approach. All possible parameters were varied to study their effect on molecular weight build-up. The effects of concentrations of A2 and B3 and the A2: B3 monomer ratio were well reflected in the molecular weight of the polymer. The structure of the B3 monomer was also found to have a significant effect on the molecular weight. The polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction and impedance spectroscopy. All the polymers registered unusual sub- Tg; and they invariably underwent decomposition at three distinct stages with significantly improved thermal stability at initial stage. The ionic conductivity of HBPU increased remarkably upon doping with KI and I2. The dye-sensitized solar cell fabricated using this polymer as electrolyte yielded an overall conversion efficiency of 3.5% upon illumination with visible light.