Toward Sulfur-Free RAFT Polymerization Induced Self-Assembly

Polymerization induced self-assembly (PISA) using methacrylate-based macromonomers as RAFT agents is an unexplored, attractive route to make self-assembled colloidal objects. The use of this class of RAFT-agents in heterogeneous polymerizations is however not trivial, because of their inherent low reactivity. In this work we demonstrate that two obstacles need to be overcome, one being control of chain-growth (propagation), the other monomer partitioning. Batch dispersion polymerizations of hydroxypropyl methacrylate in the presence of poly(glycerol methacrylate) macromonomers in water showed limited control of chain-growth. Semicontinuous experiments whereby monomer was fed improved results only to some extent. Control of propagation is essential for PISA to allow for dynamic rearrangement of colloidal structures. We tackled the problem of monomer partitioning (caused by uncontrolled particle nucleation) by starting the polymerization with an amphiphilic thermoresponsive diblock copolymer, already "phase-separated" from solution. TEM analysis showed that PISA was successful and that different particle morphologies were obtained throughout the polymerization.