Aromatic Xanthates and Dithiocarbamates for the Polymerization of Ethylene through Reversible Addition-Fragmentation Chain Transfer (RAFT)
Résumé
Aromatic xanthates and dithiocarbamates were used as chain-transfer agents (CTAs) in reversible addition-fragmentation chain transfer (RAFT) polymerizations of ethylene under rather mild conditions (≤ 80 °C, ≤ 200 bar). While detrimental side fragmentation of the intermediate radical leading to a loss of living chain-ends was observed in a previous study of alkyl xanthate CTAs, this mechanism 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 Mn of 1000 g mol-1. In contrast, the loss of chain-ends was minor for dithiocarbamates, yielding polyethylene up to Mn = 3000 g mol-1 with dispersities between 1.4 and 1.8. While all systems investigated showed significant rate retardation, the dithiocarbamates are indeed the first CTAs giving polyethylene with a high livingness via RAFT polymerization, which finally offers the possibility to readily synthesize various new polyethylene-based polymer architectures.
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