Synthesis, characterization, and H-1 NMR self-diffusion studies of dendritic aliphatic polyesters based on 2,2-bis(hydroxymethyl)propionic acid and 1,1,1-tris(hydroxyphenyl)ethane

Dendritic aliphatic polyesters of one, two, three, and four generations (M(w): 906, 1856, 3754, and 7549 g/mol) were synthesized in the convergent fashion, using 2,2-bis(hydroxymethyl)propionic acid as building block and 1,1,1-tris(hydroxyphenyl)ethane as core molecule. Dendrons of one to four generations were synthesized from the building block and in a final step coupled to the core molecule. The focal point of the dendrons was protected by a benzyl ester group and deprotected by catalytic hydrogenolysis. The esterifications were performed by conversion of the acid into the corresponding acid chloride and followed by reaction of the acid chloride with the hydroxyl groups in the presence of triethylamine and dimethylaminopyridine. The simplicity of the H-1-NMR and C-13-NMR spectras and elemental analyses suggest that pure and monodisperse dendrimers were obtained. Molecular selfdiffusion studies of first, second, third, and fourth generation dendrimers were performed, in chloroform, using pulsed-field spin echo H-1 NMR spectroscopy. The self-diffusion coefficients were calculated with the standard form of the Stejskal-Tanner equation. The effective radii of the dendrimers were estimated from the diffusion coefficients by assuming a spherical geometry for all dendrimers. The radii obtained were 7.8, 10.3, 12.6, and 17.1 Angstrom for the first, second, third, and fourth generation dendrimer, respectively.