Computational Investigation of the Aminolysis of RAFT Macromolecules

This work presents a detailed computational study and kinetic analysis of the aminolysis of dithioates, dithiobenzoates, trithiocarbonates, xanthates, and thiocarbamates, which are frequently used as chain-transfer agents for reversible addition-fragmentation chain-transfer (RAFT) polymerization. Rate coefficients were obtained from ab initio calculations, taking into account a diffusional contribution according to the encounter pair model. A kinetic model was constructed and reveals a reaction mechanism of four elementary steps: (i) formation of a zwitterionic intermediate, (ii) formation of a complex intermediate in which an assisting amine molecule takes over the proton from the zwitterionic intermediate, (iii) breakdown of the complex into a neutral tetrahedral intermediate with release of the assisting amine molecule, and (iv) amine-assisted breakdown of the neutral intermediate to the products. Furthermore, a comparative analysis indicates that the alkanedithioates and dithiobenzoates react the fastest, followed, respectively, by xanthates and trithiocarbonates, which react almost equally fast, and dithiocarbamates, which are not reactive at typical experimentally used conditions.