Dispersion RAFT polymerization: comparison between the monofunctional and bifunctional macromolecular RAFT agents

Bifunctional macromolecular RAFT (macro-RAFT) agent mediated polymerization affords one-step synthesis of the BAB triblock copolymer, which has special morphology. However, the bifunctional macro-RAFT agent mediated polymerization under heterogeneous conditions is rarely reported. In this contribution, the dispersion RAFT polymerizations of styrene in a methanol–water mixture mediated with poly(ethylene glycol) based monofunctional and bifunctional macro-RAFT agents, which afford the AB diblock copolymer of poly(ethylene glycol)- block -polystyrene ( m PEG- b -PS) and the BAB triblock copolymer of polystyrene- block -poly(ethylene glycol)- block -polystyrene (PS- b -PEG- b -PS), respectively, are compared. It is found that these two dispersion RAFT polymerizations have similar polymerization rates, and almost full monomer conversion can be achieved. The molecular weight of both the m PEG- b -PS diblock copolymer and the PS- b -PEG- b -PS triblock copolymer linearly increases with the monomer conversion, whereas the control over the polydispersity index (PDI) of the PS- b -PEG- b -PS triblock copolymer is not as good as that of the m PEG- b -PS diblock copolymer. The monofunctional macro-RAFT agent mediated dispersion polymerization affords the in situ synthesis of m PEG- b -PS colloidal nanoparticles, which can be uniformly distributed in the polymerization medium and whose size increases with the extension of the solvophobic PS block, whereas the bifunctional macro-RAFT agent mediated dispersion polymerization leads to a mixture of colloidal nanoparticles and gel-like networks of the PS- b -PEG- b -PS triblock copolymer.