Amphiphilic poly(ethylene glycol)-b-polylactide (PEG/PLA) copolymers with an aldehyde group at one end and a methacryloyl group at the other chain end were synthesized by anionic polymerization. The efficiencies of the functionalization at both ends were almost quantitative. The amphiphilic block copolymers formed micelles in aqueous media. Acetal groups on the micelle surface were quantitatively converted to aldehyde groups by an acid treatment. The end methacryloyl group located in the core of the micelle was polymerized effectively to form core−shell-type nanoparticles having reactive aldehyde groups on the surface. The size of the reactive nanoparticle was 20−30 nm which was constant with temperatures up to 60 °C. The stability of the micelle was also confirmed by a sodium dodecyl sulfate (SDS) treatment. When SDS was added to the nanosphere solution to 20 mg/mL, the particle was not collapsed. The particle was stable enough even in organic solvents. This functionalized micelle having high stability is not only expected to have wide utilities in biomedical applications (including drug delivery, diagnosis, and surface modification through the coupling of bioactive substances) but also to be of great interest as a novel supramolecular architecture.

Formation of amphiphilic poly(ethylene glycol)-b-polylactide (PEG/PLA) block copolymers was accomplished by using potassium alkoxides to initiate the anionic polymerization 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 the PEG chain end, which was later converted into an aldehyde group, were obtained. The amphiphilic block copolymers formed micelles in aqueous milieu. The conversion of acetal end groups to aldehyde groups was carried out by an acid treatment using 0.01 mol L-1 hydrochloric acid. The extent of the conversion attained was >90%, without any side reaction such as aldol condensation. The micellar structure may play an important role in preventing a possible aldol condensation between the neighboring two aldehyde groups at the PEG chain end. From dynamic light scattering measurements, no angular dependence of the scaled characteristic line width was observed in the case of the acetal-PEG/PLA(52/56) micelle, suggesting the spherical structure. The diameter and polydispersity factor of the polymeric micelle were influenced by the molecular weights and the composition of two components of the block copolymer. The block copolymer with the molecular weight of 5200 for PEG and 5600 for PLA was a most suitable balance for micelle formation with narrow distribution. Actually, the diameter and polydispersity factor (μ/Γ2) of acetal-PEG/PLA(52/56), determined by a cumulative method, were 33 nm and 0.03, respectively. No change in the micelle size and shape was observed before and after the conversion of the acetal end groups to aldehyde groups on the micelle. The critical micelle concentrations (cmc) of the polymeric micelle was 2−4 mg L-1, as determined by fluorescence spectroscopy using pyrene. This functionalized micelle, in particular the one carrying terminal aldehyde groups, is expected to have a wide utility not only in biomedical applications (e.g., drug delivery, diagnosis, and surface modification through the coupling of bioactive substances), but also for the construction of the supramolecular architecture.

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Poly(ethylene glycol) possessing a polymerizable vinylbenzyl group at one end and a carboxylic acid group at the other end was synthesized via the anionic polymerization of ethylene oxide. 1H NMR, SEC, and MALDI-TOF-MS studies confirmed that each poly(ethylene glycol) chain quantitatively possessed vinylbenzyl and carboxyl end groups. Emulsion polymerization of 2-(diethylamino)ethyl methacrylate was carried out to obtain a nanometric-sized gel (nanogel) in the presence of a cross-linking agent such as ethylene dimethacrylate, using the obtained α-vinylbenzyl-ω-carboxy-PEG as a stabilizing reagent. The size of the obtained nanogels was controllable in the range between 50 and 680 nm. The nanogel was confirmed to have a PEG shell layer with a carboxylic acid group at the distal end of each PEG strands from the ζ-potential measurement at varying pHs. The pH-sensitive swelling/deswelling behavior of the nanogels was studied by dyanmic light scattering to confirm their volume phase transition at a pH around 7.0. These prepared nanogels are expected to have potential utility in applications such as diagnostics and controlled drug releasing devices.