Synthesis and micellar characteristics of dendron-PEG conjugates.

Urethane-amide dendrons of up to the third generation were synthesized via a convergent route. These dendrons were coupled with MeO-PEG (Mn = 2000), and the micellar characteristics of dendron-PEG conjugates in water were investigated. The conjugates with the second or third generation dendron (PEG-2GOc and PEG-30c) formed micellar aggregates in an aqueous phase. However, the conjugate with the first generation dendron (PEG-1GOc) did not exhibit micellar aggregates detectable by dynamic light scattering possibly due to the high ratio of the hydrophilic moiety to hydrophobic periphery. The critical aggregation concentrations of PEG-2GOc and PEG-3GOc determined by fluorescence techniques were 7.5 and 2.0 mg/L, respectively. The mean diameters of the micelles ofPEG-2GOc and PEG-3GOc, measured by dynamic light scattering, were 90 and 170 nm. The partition equilibrium constants (Kv) of pyrene in the micellar solution increased by increasing the size of the dendritic block, for example, 6.17 x 10(4) for PEG-2GOc and 1.58 x 10(5) for PEG-3GOc. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.107 for PEG-2GOc and 0.178 for PEG-3GOc. When the third generation dendritic moiety is incorporated into the conjugates, the Kv and r values become comparable to those for typical block copolymer micelles.