Controlled Cationic Polymerization with Organotellurium Catalysts Utilizing Redox-Mediated Chalcogen Bonding Interaction

The electrochemical oxidation behavior of organotellurium compounds (DAnT, POxT, PThT, and PAzT) and the structure–property relationships of the resulting cationic species were evaluated by cyclic voltammetry and electro spin resonance measurements and density functional theory calculations. [POxT₂]²⁺ obtained from POxT was found to have a highly active chalcogen bonding (ChB) potency as evidenced by large V_s,max value (186.4 kcal·mol^–1). While neutral POxT has no catalytic activity, the electrochemically generated [POxT₂]²⁺ by applying an oxidation potential at 0.68 V vs Ag/Ag⁺ can activate the carbon–chlorine bond at the propagating chain ends of p-methylstyrene (pMeS) through the ChB interaction, resulting in a complete monomer conversion at 0 °C in 1 h to give poly(pMeS) with the theoretical molecular weight (M_n = 6100) and relatively narrow molecular weight distribution (M_w/M_n = 1.49). PAzT could not bring about the polymerization of pMeS, but p-methoxystyrene (pMOS) with the higher cationic polymerization ability was smoothly consumed to afford poly(pMOS) having M_n of 9400 and M_w/M_n of 1.94. The counteranion of supporting electrolyte influenced the polymerization behavior; namely, the application of Bu₄NPF₆ induced the controlled polymerization of pMeS and the polymer molecular weight could be determined by the monomer feed ratio. Importantly, the electrochemical control over polymer chain growth was achieved reversibly by switching the direction of current flow in the electrochemical cell between 0.68 V (ON state) and −0.30 V (OFF state).