One-Pot Synthesis of Dendritic Poly(amide-urea)s via Curtius Rearrangement. 2. Synthesis and Characterization of Dendritic Poly(amide-urea)s

Dendritic poly(amide-urea)s from the first to fourth generations with a very narrow molecular weight distribution were prepared from 1,1,1-tris(4-carboxymethyloxyphenyl)ethane as a core molecule, using aminodicarboxylic acid and aminodicarbonyl azide as two AB 2 monomers in a one-pot procedure. This procedure involves activation of end carboxyl groups with a condensing agent, diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate, condensation of the active amide with aminodicarbonyl azide, the Curtius rearrangement in the presence of aminodicarboxylic acid, and, finally, capping of the end groups with p - tert -butylaniline. All dendritic polymers were obtained quantitatively and fully characterized by elemental analysis and IR and NMR spectroscopies. Number average molecular weights ( M n ) of dendritic poly(amide-urea)s were estimated by end group analysis, and each dendritic poly(amide-urea) had M n close to the calculated value. Degrees of branching for the second and third generation dendritic polymers were found to be 0.93 and 0.90, respectively by 1 H NMR spectroscopy.