Temperature-Sensitive Nanoparticle-to-Vesicle Transition of ABC Triblock Copolymer Corona–Shell–Core Nanoparticles Synthesized by Seeded Dispersion RAFT Polymerization

A new kind of heterogeneous RAFT polymerization called seeded dispersion RAFT polymerization to prepare triblock copolymer corona–shell–core nanoparticles of the temperature-sensitive poly(N,N-dimethylacrylamide)-block-polystyrene-block-poly[N-(4-vinylbenzyl)- N,N -diethylamine] (PDMA-b-PS-b-PVEA) is proposed, and the reversible nanoparticle-to-vesicle transition of the triblock copolymer is investigated. Well-controlled seeded dispersion RAFT polymerization as indicated by the pseudo-first-order kinetics, the linear increase in the triblock copolymer molecular weight with the monomer conversion and the narrow molecular weight distribution of the synthesized triblock copolymer was performed, and triblock copolymer corona–shell–core nanoparticles, in which the temperature-sensitive poly[N-(4-vinylbenzyl)- N,N -diethylamine] (PVEA) block forms the core, the solvophobic polystyrene block forms the shell, and the solvophilic poly(N,N-dimethylacrylamide) block forms the corona, were prepared. When the corona–shell–core nanoparticles were dispersed in alcoholic solvent at temperature below the lower critical solution temperature (LCST) of the core-forming PVEA block, the nanoparticle-to-vesicle transition occurred, and the unsymmetrical ABC triblock copolymer vesicles were formed. The nanoparticle-to-vesicle transition is ascribed to the initial nanoparticle swelling in the alcoholic solvent and the subsequent out-migration of the core-forming PVEA block from the core layer to corona, which was confirmed by the real-time 1H NMR analysis and XPS analysis. The parameters affecting the nanoparticle-to-vesicle transition were investigated, and it was found that the nanoparticle-to-vesicle transition took place in the alcoholic solvent at temperature below LCST when the triblock copolymer containing a long core-forming PVEA block.