Effects of Diffusion‐Controlled Radical Reactions on RAFT Polymerization

The ‘livingness’ of a controlled radical polymerization process such as reversible addition–fragmentation transfer polymerization (RAFT) depends on the rapid deactivation of propagating radicals (the radical addition reaction in RAFT) that suppresses radical termination reactions. However, at high monomer conversions when the polymerization system becomes viscous, polymer chains may experience diffusion limitations and the radical reactions (radical addition and termination) readily become diffusion controlled. The effects of the diffusion‐controlled reactions on the RAFT kinetics and molecular‐weight development are investigated in this work using a modeling approach. It is demonstrated that the diffusion‐controlled radical termination accelerates the polymerization rate and improves the control of polymer molecular weight, while the diffusion‐controlled radical addition also accelerates the rate but broadens the molecular‐weight distribution. This model elucidates the magnitudes and changes for various types of chains involved in the RAFT, i.e., propagating radical chain, adduct radical chain, dormant chain, and dead chain. Polydispersity vs conversion of diffusion‐controlled radical termination (left) and diffusion‐controlled radical addition (right). magnified image Polydispersity vs conversion of diffusion‐controlled radical termination (left) and diffusion‐controlled radical addition (right).