Photoinduced metal free strategies for atom transfer radical polymerization

Photoinduced metal-free Atom Transfer Radical Polymerization (ATRP) processes have recently received interest as they paved the way for the synthesis of precision polymeric materials with topological and temporal control under metal-free conditions. Herein, two series of photosensitizers operating by oxidative and reductive quenching mechanisms are described. In the former case, the excited states of polynuclear aromatic compounds such as phenothiazines, perylene, pyrene, dihydrophenazines, phenoxazines and thiophene derivatives undergo electron transfer reaction with alkyl halides to form initiator radicals. In the reductive pathway, however, initiating radicals are formed through electron transfer reaction of photoexcited dyes and conventional Type II photoinitiators such as benzophenone and thioxanthone together with electron source amines and alkyl halides. The mechanistic details are evaluated and potentials and limitation of these systems are presented.