An Efficient Route for the Synthesis of Hyperbranched Polymers and Dendritic Building Blocks Based on Urea Linkages

摘要

A highly efficient synthetic route, based on the quantitative reaction be- tween amine and isocyanate functionalities, was used successfully for the synthesis of hyperbranched polymers and dendritic building blocks based on urea linkages. The thermal decomposition of 3,5-diamino benzoyl azide or 5-amino isophthaloyl azide generated in situ the corresponding phenyl isocyanates, which were then polymerized to give wholly aromatic hyperbranched polyureas. Hyperbranched polyurea with amine chain ends was soluble in common organic solvents. The degree of branching, as calculated with 1H NMR, was 0.55. Diethyl 5-amino isophthalate and Boc-protected 5-amino isophthaloyl azide were used for the successful stepwise synthesis of dendritic wedges based on urea linkages. The thermal generation of the isocyanate functionality with gaseous nitrogen as the side product and its quantitative reaction with amine groups were the salient features of this convergent synthesis. This eliminated the use of chromatographic purification, an inherent part of other convergent growth ap- proaches, and made it a very efficient synthetic route for the synthesis of dendritic wedges. The products were characterized by 1H NMR, 13C NMR, and electron spray mass spectroscopy (ESMS) techniques.