Synthesis of Polystyrene-block-Poly(4-vinylpyridine) Ellipsoids through Macro-RAFT-Agent-Mediated Dispersion Polymerization: The Solvent Effect on the Morphology of the In Situ Synthesized Block Copolymer Nanoobjects

The solvent character affecting the morphology of the block copolymer nanoobjects prepared through the macro-RAFT-agent-mediated dispersion polymerization is discussed. It is found that, in the polystyrene macro-RAFT-agent-mediated dispersion polymerization of 4-vinylpyridine in the solvent of the toluene/cyclohexane mixture, the toluene/cyclohexane weight ratio in the polymerization solvent highly affected the morphology of the in situ synthesized polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) nanoobjects, and nanospheres are formed in pure toluene and ellipsoids are formed in the toluene/cyclohexane mixture containing 10–20 wt% cyclohexane, respectively. The formation of the PS-b-P4VP ellipsoids is explored by checking the polymerization kinetics and the morphology of the in situ synthesized PS-b-P4VP nanoobjects at different monomer conversion. It was revealed that the formation of ellipsoids is possibly through the nanosphere–nanosphere fusion and/or the nanosphere-to-rod transition with the extension of the poly(4-vinylpyridine) block during the dispersion reversible addition–fragmentation chain transfer (RAFT) polymerization. This study demonstrates that tuning the solvent character may be a promising method to tune the morphology of block copolymer nanoobjects under dispersion RAFT polymerization condition.