Synthesis of star polymers using RAFT polymerization: What is possible?

Various pathways to generate star polymers using reversible addition?fragmentation transfer (RAFT) are discussed. Similar to other polymerization techniques, star polymers can be generated using arm-first and core-first approaches. Unique to the RAFT process is the subdivision of the core-first approach into the R-group and Z-group approaches, depending on the attachment of the RAFT agent to the multifunctional core. The mechanism of the R- and Z-group approaches are discussed in detail and it is shown that both techniques have to overcome difficulties arising from termination reactions. Termination reactions were found to broaden the molecular weight. However, these side reactions can be limited by careful design of the synthesis. Considerations include RAFT and radical concentration, number of arms, type of RAFT agent and monomer. Despite obvious challenges, the RAFT process is highly versatile, allowing the synthesis of novel polymer architectures such as poly(vinyl acetate) and poly(vinyl pyrrolidone) star polymers.