DYNAMICS OF CHAIN EXCHANGE BETWEEN SELF-ASSEMBLED DIBLOCK COPOLYMER MICELLES OF POLY(ETHYLENE OXIDE)-block-POLYLACTIDE STUDIED BY DIRECT NONRADIATIVE EXCITATION ENERGY TRANSFER

摘要

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.