Collect. Czech. Chem. Commun. 2005, 70, 1811-1828

Dynamics of Chain Exchange Between Self-Assembled Diblock Copolymer Micelles of Poly(ethylene oxide)-block-Polylactide Studied by Direct Nonradiative Excitation Energy Transfer

Štěpán Popelkaa, Luďka Machováa, František Rypáčeka, Milena Špírkováa, Miroslav Štěpánekb, Pavel Matějíčekb and Karel Procházkab,*

a Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, 162 06 Prague 6, Czech Republic
b Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Albertov 6, 128 40 Prague 2, Czech Republic


A series of diblock poly(ethylene oxide)-block-polylactide copolymers with fairly narrow distribution of molar masses and compositions was prepared and characterized. The copolymers form multimolecular spherical micelles in 1,4-dioxane-water mixtures. The chain exchange between micelles formed by fluorescence-labeled copolymers was studied by direct nonradiative excitation energy transfer (NRET) fluorescence measurements in water-rich media containing 10 vol.% of 1,4-dioxane. The equilibration rate, i.e., the rate of unimer chain exchange between micelles obeys basically the theoretically predicted scaling relations. It slows down with the length of soluble blocks (a quadratic decrease) and considerably (an exponential decrease) with the length of insoluble chains. Scaling exponents were found lower than those predicted. The study shows that nanoparticle systems based on poly(ethylene oxide)-block-polylactide copolymers with required properties for various biomedical applications can be designed, prepared and their properties can be optimized.

Keywords: Block copolymers; Self assembly; Micelles; Biodegradable polymers; Light scattering; Fluorescence spectroscopy; Atomic force microscopy.

References: 38 live references.