Amphiphilic diblock copolymers based on poly(2-ethyl-2-oxazoline) and poly(1,3-trimethylene carbonate): Synthesis and micellar characteristics

Amphiphilic diblock copolymers with various block compositions were synthesized on the basis of poly(2-ethyl-2-oxazoline) (PEtOz) as a hydrophilic block and poly(1,3-trimethylene carbonate) (PTMC) as a hydrophobic block. Their aqueous solutions were characterized using fluorescence techniques and dynamic light scattering. The block copolymers formed micelles with critical micelle concentrations (cmc's) in the range 2.8-25 mg/L in an aqueous phase. As the length of the hydrophobic PTMC block became longer, lower cmc values were generated. The mean diameters of the micelles were in the range 199-210 nm, with a narrow distribution. The partition equilibrium constants (K_v) of pyrene in the micellar solutions of the block copolymers were 0.91×10⁵-1.61×10⁵. The K_v 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) in PEtOz-PTMC solutions were 0.292-0.302. The anisotropy values were not significantly influenced by the length of the hydrophobic block. The micelles underwent hydrogen bonding at pH<3.6 with poly(acrylic acid) resulting in polymer complex precipitates, which could be reversibly dispersed as micelles at pH>3.9.