Seeded dispersion RAFT polymerization and synthesis of well-defined ABA triblock copolymer flower-like nanoparticles

A new kind of heterogeneous RAFT polymerization named 'seeded dispersion RAFT polymerization' is proposed for the preparation of well-defined triblock copolymer flower-like nanoparticles. Concentrated seed-nanoparticles of the amphiphilic polystyrene-block-poly(dimethylacrylamide) diblock copolymer including the RAFT agent Z-group at the terminal end of the solvophilic poly(dimethylacrylamide) block are prepared by diblock copolymer micellization in a ternary solvent mixture containing styrene monomer. Well-controlled seeded dispersion RAFT polymerization in the presence of the seed-nanoparticles is achieved, which is indicated by the linear increase in molecular weight with monomer conversion and the narrow molecular weight distribution of the synthesized polystyrene-block-poly(dimethylacrylamide)-block-polystyrene (PS-b-PDMA-b-PS) triblock copolymers. Compared with a soluble macro-RAFT agent mediated dispersion polymerization, the seeded dispersion RAFT polymerization is faster and either a very short induction time or no induction time is observed. The seeded dispersion RAFT polymerization affords well-defined flower-like nanoparticles of the PS-b-PDMA-b-PS triblock copolymer in the solvent which is selective for the central PDMA block. The effect of the polymerization degree of the outer PS blocks and the central PDMA block on the size and morphology of the flower-like nanoparticles is investigated, it is concluded that the size of the flower-like nanoparticles decreases with the central PDMA block length but increases with the outer PS block length.