A Step Toward Cationic RAFT Polymerization of Less Reactive Monomers: Dithiobenzoates Bearing Electron-Withdrawing Groups as a Chain-Transfer Agents

Here, we report the new strategy for the cationic RAFT polymerization of less reactive monomers such as p-methylstyrene and styrene. This strategy implies the addition of electron-withdrawing substituents into stabilizing group of cumyl dithiobenzoate that results in the decrease the stability of cationic intermediates thus facilitating their fragmentation and cationic RAFT polymerization. Particularly, it was demonstrated that both cumyl dithiobenzoate and cumyl dithiobenzoate with trifluoromethyl substituent in Z-group activated by small amount of SnCl4 induced living cationic RAFT polymerization of p-methoxystyrene affording polymers with molecular weight up to 80,000 and 30,000 g mol-1, respectively. In contrast to unsubstiuted counterpart, cumyl dithiobenzoate with trifluoromethyl substituent in Z-group was also efficient chain transfer agent for conducting of living cationic RAFT polymerization of p-methylstyrene giving polymers with Mn up to 10,000 g mol-1 and moderate dispersity (Đ= 1.3 – 1.8), while polymerization is terminated at incomplete conversion when cumyl dithiobenzoate was used. Cumyl dithiobenzoate with trifluoromethyl substituent in conjunction with SnCl4 also induced cationic RAFT polymerization of styrene affording well-defined polystyrenes with Mn up to 5,000 g mol-1. Finally, the block copolymers of p-methylstyrene with styrene and methyl methacrylate were sucesfully synthesized via mechanistic transformation from cationic to radical RAFT polymerization.