Size control of core-shell-type polymeric micelle with a nanometer precision.

Amphiphilic polydepsipeptides having a hydrophobic poly(L-lactic acid) block and varying numbers of a hydrophilic poly(sarcosine) block ranging from 1 to 3, AB-, A2B-, and A3B-type, were prepared and studied on their molecular assemblies. The morphologies were found to be polymeric micelles for the AB- and the A3B-type polydepsipeptides, but worm-like micelles for the A2B-type polydepsipeptide. The hydrodynamic diameter of the A3B-type polydepsipeptide (22 nm) became smaller than the AB-type polydepsipeptide (34 nm). The polymeric micelle sizes composed of the AB-type polydepsipeptide were adjustable up to ca. 100 nm with incorporation of poly(L-lactic acid) into the hydrophobic core. On the other hand, with varying mixing ratio of the AB-type and A3B-type polydepsipeptides, the hydrodynamic diameters were tunable to become smaller sizes with a precise control in the range from 22 to 34 nm. The polydispersity indices of the polymeric micelles were less than 0.1, indicating that we can obtain the homogeneous polymeric micelles with diameters in the range from 20 to 100 nm under a precise control.