Synthesis and photophysical characterization of amphiphilic dendritic-linear-dendritic block copolymers

Abstract

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl-terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D-Si-1G) and second (PEO–D-Si-2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D-Si-1G and PEO–D-Si-2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D-Si-1G and PEO–D-Si-2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore-type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 104 for PEO–D-Si-1G and 9.57 × 104 for PEO–D-Si-2G). The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene were 0.06 for PEO–D-Si-1G and 0.09 for PEO–D-Si-2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 918–926, 2001