Synthesis and characterization of N-substituted hyperbranched polyureas

N,N'-disubstituted hyperbranched polyureas with methyl, benzyl, and allyl substitutents were synthesized starting from AB(2) monomers based on 3,5-diamino benzoic acid. Carbonyl azide approach, which generates isocyanate group in situ on thermal decomposition, was used for the protection of isocyanate functional groups. The N-substituted hyperbranched polymers can be considered as the new class of internally functionalized hyperbranched polyureas wherein the substituent can function either as receptor or as a chemical entity for selective transformations as a tool to tailor the properties. The chain-ends were also modified by attaching long chain aliphatic groups to fully realize the interior functionalization. This approach opens up a possible synthetic route wherein different functional substituents can be used to generate a library of internally functionalized. hyperbranched polymers. All the hyperbranched polyureas were characterized by FTIR, H-1-NMR, DSC, TGA, and size exclusion chromatography. Degree of branching in these N,N'-disubstituted hyperbranched polyureas, as calculated by H-1-NMR spectroscopy using model compounds, was found to be lower than the unsubstituted hyperbranched polyurea and is attributed to the lower reactivity of N-substituted amines compared to that of unsubstituted amines. (C) 2004 Wiley Periodicals, Inc.