Surfactant-free synthesis of amphiphilic diblock copolymer in aqueous phase by a self-stability process

Amphiphilic polymeric particles with hydrophobic cores and hydrophilic shells were prepared via living radical emulsion polymerization of styrene using a water-soluble poly(acrylamide)-based macro-RAFT agent in aqueous solution in the absence of any surfactants. Firstly, the homopolymerization of acrylamide (AM) was carried out in aqueous phase by reversible addition-fragmentation chain transfer radical polymerization (RAFT) using a trithiocarbonate as a chain transfer agent. Then the PAM-based macro-RAFT agent has been used as a water-soluble macromolecular chain transfer agent in the batch emulsion polymerization of Styrene (St) free of surfactants. The RAFT controlled growth of hydrophobic block led to the formation of well-defined poly(acrylamide)-copolystyrene amphiphilic copolymer, which was able to work as a polymeric stabilizer (self-stability). Finally, very stable latex was prepared, having no visible phase separation for several months. FTIR and H-1-NMR measurements showed that the product was the block copolymer PAM-co-PS in the form of stable latex. Atomic force microscope (AFM), transmission electron microscope (TEM), and dynamic light scattering (DLS) studies indicated that the nanoparticles have a narrow particle size distribution and the average particle hydrodynamic radius was kept in the diameter of 58 nm. Core-shell structure of the copolymer was also recorded by TEM. The mechanism of the self-stability of polymer particles during the polymerization in the absence of surfactants was studied. (C) 2008 Wiley Periodicals, Inc.