Raft Polymerization Of Styrene In The Microreactor Of Hollow Microspheres

Reversible addition-fragmentation chain transfer (RAFT) polymerization of a typical hydrophobic monomer of styrene within microreactor of shell-corona hollow microspheres of poly(styrene-co-methacrylic acid) (PS-co-PMAA) suspending in water is studied in this paper. The shell-corona hollow microspheres are synthesized by template polymerization. The synthesis involves three sequential steps including synthesis of a sacrificial core template of PS-co-PMAA core-shell microspheres by one-stage soap free emulsion polymerization, coating polymerization on the template to form coated microspheres, and formation of hollow microspheres by removing the core template. The synthesized hollow microspheres contain a hydrophilic corona of poly(methacrylic acid), which can help the hollow microspheres suspend in water and a hydrophobic microcavity in which organic molecules can be encapsulated.Since the hollow microspheres have the characters mentioned above, it can be used as microreactor suspending in water, within which RAFT polymerization of a typical hydrophobic monomer of styrene runs with a controlled manner. The microreactor-RAFT polymerization of styrene involves 3 steps. First, the mixture of monomer, initiator and RAFT agent is encapsulated within the microreactor of the PS-co-PMAA shell-corona hollow microspheres suspending in water. Second, the aqueous dispersion is heated to 70℃and RAFT polymerization of the encapsulated styrene within the microreactor is initiated. Lastly, the resultant polymer is released from the microreactor by dispersing the polymer-filled microreactor in dichloromethane (CH2Cl2). It is found that the coagulum formation can be prevented and the microreactor-RAFT polymerization runs in well controlled manner in water. That is, the value of ln([M]o/[M]) increases linearly with the increase of reaction time and the number-average molecular weight of the resultant polystyrene increases linearly with monomer conversion. The resultant polymer of polystyrene has a competitively low polydispersity index.The method is believed to be a new strategy of RAFT polymerization of hydrophobic monomer in aqueous solution.