Zero-valent metal catalyzed radical-induced adjustable removal/modification of thiocarbonylthio end groups of RAFT polymer at ambient temperature

This work describes a facile removal/modification of thiocarbonylthio end groups of RAFT-made polymers by the utilization of zero-valent copper (Cu(0)) powder/2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) under mild conditions, especially for poly(methyl methacrylate) (PMMA). At [PMMA]0/[Cu(0)]0/[ligand]0/[TEMPO]0 = 1/5/5/1.5, the molecular weights (MWs) gradually increased to twofold that of the precursor, due to the polymeric radical–polymeric radical cross coupling. While the MW remained unchanged at [PMMA]0/[Cu(0)]0/[ligand]0/[TEMPO]0 = 1/5/5/5, generating vinyl group terminated telechelic polymers via a polymeric radical–TEMPO disproportionation process. The utilization of Cu(0) wire can also remove the thiocarbonylthio end group effectively. Zero-valent iron (Fe(0)) (powder or wire) can be applied to remove/modify the thiocarbonylthio end group instead of Cu(0)/ligand with comparable results. This work provided an alternative and promising approach for an adjustable end group removal/modification of RAFT polymers, and would eventually strengthen and facilitate the potential large-scale application of RAFT-related polymers.