Computer-Aided Design of a Destabilized RAFT Adduct Radical: Toward Improved RAFT Agents for Styrene-<i>block</i>-Vinyl Acetate Copolymers

Abstract

High-level ab initio molecular orbital calculations indicate that a fluorine Z substituent significantly destabilizes the RAFT adduct radical, R‘SC·(Z)SR, relative to known Z substituents. This destabilization of the RAFT adduct radical lowers the fragmentation enthalpy relative to normal dithioesters, but without stabilizing the CS bond of the product RAFT agent, as in xanthate- or dithiocarbamate-mediated polymerization. On the basis of these calculations, it is predicted that, provided appropriate R groups are chosen, RAFT agents containing fluorine Z substituents (i.e., SC(F)SR, fluorodithioformates, or “F-RAFT” agents) should provide a basis for improved control of monomers with reactive propagating radicals (such as vinyl acetate) and should have the advantage that their CS bonds remain reactive enough for control of monomers with more stable propagating radicals (such as styrene) and hence the production of styrene−vinyl acetate copolymers.