Diblock copolymers of ethylene oxide and 1,2-butylene oxide in aqueous solution: Formation of unimolecular micelles

The dependence of log(cmc) on hydrophobic block length n was examined for EmBn copolymers (E = oxyethylene, B = oxybutylene, subscripts denote number-average block lengths in repeat units) with n in the range 30–76. Combination with published data for EmBn diblock copolymers with shorter E-blocks shows two changes of slope in the log(cmc)–n plot corresponding to the onset of unimolecular micelle formation at n ≈ 12 and completion of this process at n ≈ 30. The results are discussed with reference to published data for EmLn and EmCLn (L from d,l-lactide; CL from ɛ-caprolactone) copolymers, which show similar behaviour.