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 (M_n = 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-3Oc) 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 of PEG-2GOc and PEG-3GOc, measured by dynamic light scattering, were 90 and 170 nm. The partition equilibrium constants (K_v) of pyrene in the micellar solution increased by increasing the size of the dendritic block, for example, 6.17 × 10⁴ for PEG-2GOc and 1.58 × 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 K_v and r values become comparable to those for typical block copolymer micelles.