Amphiphilic linear PEO-dendritic carbosilane block copolymers

A new class of amphiphilic linear-dendritic diblock copolymers based on hydrophilic linear PEO and hydrophobic dendritic carbosilane were synthesized using a divergent approach at the allyl end group of the allyl-terminated PEO. The amphiphilic nature of these block copolymers was highly dependent on the size of the hydrophobic dendritic block. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO-Si-1G) and, the second (PEO-Si-2G) generation of dendritic carbosilane blocks form micelles in an aqueous phase. The critical micelle concentrations of PEO-Si-1G and PEO-Si-2G, determined by a fluorescence technique, were 82.6 and 2.3 mg/L, respectively. The mean diameters of the micelles of PEO-Si-1G and PEO-Si-2G, measured by dynamic light scattering, were 120 and 170 nm. The partition equilibrium constants, K_v, of pyrene in the micellar solution increased by increasing the size of the dendritic block, e.g., 9.13 × 10³ for PEO-Si-1G and 1.75 × 10⁵ for PEO-Si-2G. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.08 for PEO-Si-1G and 0.10 for PEO-Si-2G. The r values were lower than the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core is lower than those of other polymeric micelles.