Synthesis and properties of aromatic polyamide dendrimers with polyhedral oligomeric silsesquioxane cores

Aromatic polyamide dendrimers possessing polyhedral oligomeric silsesquioxane (POSS) cores were synthesized up to the sixth generation. Octa(n-propylamine)-POSS and 3,5-bis(trifluoroacetamido)benzoic acid were prepared as an eight-functional core and an AB2 building block, respectively. Condensation of the core with the AB2 building block, followed by deprotection via transamidation with hydrazine, was conducted to provide the G1 dendrimer. The other dendrimers up to the sixth generation were prepared in a similar manner. All dendrimers were obtained in high yields (>90%) via a simple precipitation process without the need for tedious purification steps such as column chromatography. The structures of the dendrimers were characterized by NMR, FT-IR, MALDI-TOF mass spectroscopy, and light scattering measurements. The dynamic light scattering and AFM measurements suggest that the dendrimers have squashed shapes on the substrate even for the sixth generation. The trifluoroacetamide-terminated dendrimers show specific fluorescence emission at 445 nm under 330 nm irradiation and the emission intensity is increased with increasing the generation number. The generation dependence of the emission intensity is similar to that of the intrinsic viscosity of the dendrimers.