Aromatic Xanthates and Dithiocarbamates for the Polymerization of Ethylene through Reversible Addition-Fragmentation Chain Transfer (RAFT)

Aromatic xanthates and dithiocarbamates were used as chain-transfer agents (CTAs) in reversible addition-fragmentation chain-transfer (RAFT) polymerizations of ethylene under milder conditions (≤80 °C, ≤200 bar). While detrimental side fragmentation of the intermediate radical leading to loss of living chain-ends was observed before with alkyl xanthate CTAs, this was absent for the aromatic CTAs. The loss of living chain-ends was nevertheless detected for the aromatic xanthates via a different mechanism based on cross-termination. Narrow molar-mass distributions with dispersities between 1.2 and 1.3 were still obtained up to number average molar masses M_n of 1000 g mol^-1 . The loss of chain-ends was minor for dithiocarbamates, yielding polyethylene up to M_n =3000 g mol^-1 with dispersities between 1.4 and 1.8. While systems investigated showed significant rate retardation, the dithiocarbamates are the first CTAs giving polyethylene with a high livingness via RAFT polymerization.