Radical-induced oxidation of RAFT agents : a kinetic study

Radical-induced oxidn. of reversible addn.-fragmentation chain transfer (RAFT) agents is studied with respect to the effect of mol. structure on oxidn. rate. The radicals are generated by homolysis of either azobisisobutyronitrile or alkoxyamine and transformed in situ immediately into peroxy radicals through transfer to mol. oxygen. The oxidn. rate depends on the structure of Z- and R-group of thiocarbonylthio compds. For dithioesters with identical Z-Ph substituent, the oxidn. rate decreases in the order of cyanoisopropyl (-C(Me)2CN) > cumyl (-C(Me)2Ph) > phenylethyl (-CH(Me)Ph) > 2-methoxy-1-methyl-2-oxoethyl (-CH(Me) -C(=O)OCH3) > benzyl (-CH2Ph). For dithioesters with identical R-group, the oxidn. rate decreases in the order of Z = phenyl- ∼ benzyl- > RS- (trithiocarbonates) > RO- (xanthates). The stability of the RAFT agents toward oxidn. correlates well with the chain transfer abilities as those previously reported by Rizzardo and coworkers. The priority of the oxidn. reaction over the RAFT process, and the subsequent influence on RAFT polymn. are also studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. [on SciFinder(R)]