Macro-RAFT agent mediated dispersion polymerization: the monomer concentration effect on the morphology of the in situ synthesized block copolymer nano-objects

The monomer concentration affecting the morphology of the in situ synthesized block copolymer nanoobjects during the macro-RAFT agent mediated dispersion polymerization is investigated. It is found that the monomer concentration exerts a great influence on both the polymerization kinetics of the poly(ethylene glycol) trithiocarbonate macro-RAFT agent mediated dispersion polymerization and the morphology of the in situ synthesized nano-objects of the poly(ethylene glycol)-block-polystyrene (PEG-b-PS) diblock copolymer. The poly(ethylene glycol) trithiocarbonate macro-RAFT agent mediated dispersion polymerization of styrene in an alcoholic solvent at 50% high monomer concentration follows similar kinetic behaviour to homogeneous RAFT polymerization as indicated by the linear ln([M](0)/[M])-time plot, and good control both on the molecular weight of the PEG-b-PS diblock copolymer and the molecular weight distribution is achieved. With the extension of the PS block, the morphology of the in situ synthesized PEG-b-PS nano-objects changes from the porous nanospheres to the bicontinuous nanospheres and finally to the entrapped vesicles, which is much different from the dispersion RAFT polymerization at low monomer concentrations. Our results demonstrate that the monomer concentration is an important parameter affecting the morphology of the in situ synthesized block copolymer nano-objects.