Synthesis and Micellar Characterization of Amphiphil

ABSTRACT: Amphiphilic diblock copolymers were synthesized based on poly(2-ethyl-2-oxazoline) (PEtOz)
as a hydrophilic block and aliphatic polyesters such as poly(L-lactide) (PLA) or poly(-caprolactone) (PCL)
as a hydrophobic block. Their micellar characteristics in an aqueous phase were investigated by using
dynamic light scattering and fluorescence techniques. The block copolymers formed micelles in the aqueous
phase with critical micelle concentrations (cmcs) in the range of 1.0-8.1 mg/L. The cmc values become
lower upon increasing the length of the hydrophobic block. The mean diameters of the micelles were in
the range of 108-192 nm, with a narrow distribution. In general, the micelle size increased as the
hydrophobic PLA or PCL block became larger. The partition equilibrium constants, Kv, of pyrene in the
micellar solutions of the block copolymers were from 1.79 105 to 5.88 105. For each block copolymer
system of PEtOz-PLA or PEtOz-PCL, the Kv value increased as the length of the hydrophobic block
increased. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were
0.265-0.284 in PEtOz-PLA solution and 0.189-0.196 in PEtOz-PCL solution. The anisotropy values
of PEtOz-PLAs were higher than those of PEtOz-PCLs. The anisotropy values were independent of the
length of the hydrophobic block when the chemical structures of the hydrophobic blocks were identical.
The micelles underwent hydrogen bonding at pH <3.5 with poly(acrylic acid), which produced polymer
complex precipitates that could be reversibly dispersed as micelles at pH >3.8.