Polymeric nanocapsules were synthesized by encapsulating extruded vesicles of dimethyldioctadecyl ammonium bromide (DODAB) using a reversible addition-fragmentation chain transfer (RAFT)-based encapsulation approach. Random copolymers containing acrylic acid and butyl acrylate units were first synthesized by RAFT in solution using dibenzyl trithiocarbonate (DBTTC) as the RAFT agent. These anionic copolymer chains were subsequently adsorbed onto the surface of cationic DODAB vesicles and then chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryogenic transmission electron microscopy (cryo-TEM) characterizations demonstrate the successful formation of nanocapsules.
Single montmorillonite platelets have been successfully encapsulated by polymer through both a conventional and a reversible addition-fragmentation chain transfer (RAFT) based emulsion polymerization. For both synthetic methods, the encapsulation process basically consisted of three steps: (i) adsorption of cationic RAFT copolymers (RAFT approach) or surfactant (conventional approach); (ii) high shear dispersion of the stabilized clay in aqueous solutions; (iii) starved-feed addition of monomers starting the polymerization. In the conventional approach, the morphology of the latex/clay nanocomposites was close to the dumbbell shapes previously reported and did not depend on the presence of organic modifier as evidenced by cryotransmission electron microscopy and scanning electron microscopy. In the RAFT approach a completely different morphology was obtained which has been coined the cornflake morphology. With these two new approaches we can control the orientation of the clay platelets inside the latex particles which in turn can control the orientation of the clay platelets in a film. A perspective on possible applications of these different morphologies is given, e.g. their use in high barrier coatings.
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