RAFT-Mediated Emulsion Polymerization of Styrene in Water using a Reactive Polymer Nanoreactor

We have demonstrated a nanoreactor methodology to produce polystyrene nanoparticles with narrow molecular weight distributions (MWD) and control over the final particle size distributions. Our reactive thermoresponsive diblock copolymer nanoreactor is an ideal setting to carry out otherwise difficult reversible addition–fragmentation chain transfer (RAFT)-mediated polymerizations, resulting in surfactant-free nanoparticles that can be tuned to size and MWD. By confining the MacroRAFT agent within the nanoreactor, the poor P(DMA68-b-NIPAM73)-SC(=S)SC4H9 (PNIPAM) leaving group on the MacroCTA behaves as a highly active MacroCTA through kinetic rather than thermodynamic control. The Mn was close to theory with low polydispersity indices (PDIs) (<1.2). The particle size increased with the ratio of styrene to nanoreactors and with very narrow particle size distributions. However, we found that there was a limited amount of styrene monomer that can be encapsulated into the nanoreactor, leading to polymerizations stopping well before full conversion. This problem was overcome through the addition of a non-reactive thermoresponsive diblock copolymer, which resulted in Mns close to 340 K and low PDIs. Manuscript received: 15 April 2009. Manuscript accepted: 15 July 2009.