| Abstract
| - Formation of amphiphilic poly(ethyleneglycol)-b-polylactide (PEG/PLA) blockcopolymerswas accomplished by using potassium alkoxides to initiate the anionicpolymerization of ethylene oxide,with the living chain end initiating the polymerization of lactide.By using potassium 3,3-diethoxypropoxide as an initiator, block copolymers with an acetal moiety at thePEG chain end, which was laterconverted into an aldehyde group, were obtained. The amphiphilicblock copolymers formed micelles inaqueous milieu. The conversion of acetal end groups to aldehydegroups was carried out by an acidtreatment using 0.01 mol L-1 hydrochloricacid. The extent of the conversion attained was >90%,withoutany side reaction such as aldol condensation. The micellarstructure may play an important role inpreventing a possible aldol condensation between the neighboring twoaldehyde groups at the PEG chainend. From dynamic light scattering measurements, no angulardependence of the scaled characteristicline width was observed in the case of the acetal-PEG/PLA(52/56)micelle, suggesting the sphericalstructure. The diameter and polydispersity factor of the polymericmicelle were influenced by themolecular weights and the composition of two components of the blockcopolymer. The block copolymerwith the molecular weight of 5200 for PEG and 5600 for PLA was a mostsuitable balance for micelleformation with narrow distribution. Actually, the diameter andpolydispersity factor (μ/Γ2) of acetal-PEG/PLA(52/56), determined by a cumulative method, were 33 nm and0.03, respectively. No change inthe micelle size and shape was observed before and after the conversionof the acetal end groups toaldehyde groups on the micelle. The critical micelleconcentrations (cmc) of the polymeric micelle was2−4 mg L-1, as determined by fluorescencespectroscopy using pyrene. This functionalized micelle,inparticular the one carrying terminal aldehyde groups, is expected tohave a wide utility not only inbiomedical applications (e.g., drug delivery, diagnosis, and surfacemodification through the coupling ofbioactive substances), but also for the construction of thesupramolecular architecture.
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