In situ synthesis of diblock copolymer nano-assemblies via dispersion RAFT polymerization induced self-assembly and Ag/copolymer composite nanoparticles thereof

Abstract

One pot in situ preparation of poly(acrylic acid)-block-polystyrene (PAA-b-PSt) or poly(acrylic acid)-block-poly(acrylic acid-ran-styrene) (PAA-b-P(AA-r-St)) diblock copolymer nano-objects with multiple morphologies was developed through dispersion RAFT polymerization in ethanol/water mixtures mediated by hydrophilic poly(acrylic acid) (PAA)-based macromolecular RAFT agents. The polymerization shows characteristic features of “living”/controlled radical polymerization and the experimental results are confirmed by transmission electron microscopy (TEM), gel permeation chromatography (GPC), dynamic light scattering (DLS) and ¹H NMR. The effects of various parameters including the monomer conversion, St/AA feed ratio and solvent composition on the morphologies of PAA-b-PSt diblock copolymer nano-objects were investigated in detail. A faster polymerization rate was observed with increasing content of water in mixture solvents, and three stages with two clear turning points at which the rate was enhanced were observed during the polymerization process. Spherical micelles, worms, vesicles, and lacunal nanospheres have been obtained for PAA-b-PSt with the extension of the PSt block in 70/30, 80/20 and 90/10 w/w ethanol/water mixtures. Our results demonstrate that the interesting lacunal morphology of PAA-b-PSt diblock copolymer assembly can be successfully prepared and tuned at high styrene conversion. More interestingly, the residual AA, which was introduced to prepare the random P(AA-r-St) block, can promote the evolution of the copolymer aggregate morphology from spherical micelles to worms and pure vesicles in 90/10 and 80/20 w/w ethanol/water mixtures. The copolymerization of the residual hydrophilic monomer can be a convenient and effective method to tune the morphology and size of the block copolymer aggregates via polymerization-induced self-assembly (PISA). Finally, the in situ formation of silver/polymer composite nanoparticles was demonstrated, suggesting excellent applications in catalysis.