Starting from 3,5‐diamino benzoic acid, 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzyl ether, an AB2‐type blocked isocyanate monomer with flexible ether group, and 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzoate, an AB2‐type blocked isocyanate monomer with ester group, were synthesized for the first time. Using the same starting compound, 3,5‐bis{(benzoxycarbonyl)imino}benzylalcohol, an AB2‐type blocked isocyanate monomer, was synthesized through a highly efficient short‐cut route. Step‐growth polymerization of these monomers at individually optimized experimental conditions results in the formation of hyperbranched polyurethanes with and without ether and ester groups. Copolymerizations of these monomers with functionally similar AB monomers were also carried out. The molecular weights of the polymers were determined using GPC and the values (Mw) were found to vary from 1.5 × 104 to 1.2 × 106. While hyperbranched polyurethanes having no ether or ester group were found to be thermally stable up to 217 °C, hyperbranched poly(ether–urethane)s and poly(ester–urethane)s were found to be thermally stable up to 245 and 300 °C, respectively. Glass transition temperature (Tg) of polyurethane was reduced significantly when introducing ether groups into the polymer chain, whereas Tg was not observed even up to 250 °C in the case of poly(ester–urethane). Hyperbranched polyurethanes derived from all the three different AB2 monomers were soluble in highly polar solvents and the copolymers showed improved solubility. Polyethylene glycol monomethyl ether of molecular weight 550 and decanol were used as end‐capping groups, which were seen to affect the thermal, solution, and solubility properties of polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3877–3893, 2007

methylidene]aminophenoxyhexylgbenzene-1,3-dicarboxylate -a novel A 2 diol monomer -and a series of new blocked isocyanates (B 3 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 A 2 þ B 3 approach. All possible parameters were varied to study their effect on molecular weight build-up. The effects of concentrations of A 2 and B 3 and the A 2 : B 3 monomer ratio were well reflected in the molecular weight of the polymer. The structure of the B 3 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-T g ; 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 I 2 . The dye-sensitized solar cell fabricated using this polymer as electrolyte yielded an overall conversion efficiency of 3.5% upon illumination with visible light.

A new B3‐type blocked isocyanate core and AB2‐type building block molecules containing bis‐indole moiety were synthesized via a scalable synthetic routes. Starting with these molecules, amine‐ and blocked isocyanate‐terminated polyurethane dendrimers up to third generation were build‐up using (i) a simple urethane interchange reaction, (ii) deprotection of amine and (iii) efficient conversion of amine into blocked isocyanate groups. The structural integrity of the core, building block and their intermediates were verified using FT‐IR, 1H‐NMR, and 13C‐NMR spectroscopy and HR‐MS technique. The structure and molecular weight of blocked isocyanate‐terminated dendrimers were confirmed using 1H‐NMR spectra and size exclusion chromatography with multi angle laser light scattering detector (SEC‐MALLS) technique respectively whereas the structure of all other dendrimers were confirmed using FT‐IR, 1H‐NMR, and 13C‐NMR spectroscopy. Dye‐sensitized solar cells (DSSC) were fabricated using these dendrimers as electrolytes; the DSSC fabricated with G3 dendrimer yielded an overall energy conversion efficiency (η) of 6.32 % upon illumination with 1 sun visible light.

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