Size-Tunable Nanoparticle Synthesis by RAFT Polymerization in CO2-Induced Miniemulsions

A novel environmentally friendly low-energy emulsification method that relies on pressurization with CO2 to low pressure has been applied to reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene-in-water miniemulsions with the anionic surfactant Dowfax 8390. This method circumvents traditional high-energy homogenization, and over a certain CO2 pressure range, a transparent miniemulsion is formed. RAFT polymerization of styrene using benzyldodecyl trithiocarbonate and the aqueous phase initiator VA-044 was carried out successfully in CO2-induced miniemulsions at 50 degrees C with good control/livingness. Interestingly, the particle size could be conveniently tuned via the CO2 pressure without altering the recipe, with 6.00, 6.50, and 7.50 MPa generating number-average particle diameters of 98, 89, and 48 nm, respectively, at, similar to 70% conversion. The smallest particle size corresponded to the pressure range within which the emulsion was transparent.