Additive-Triggered Chain Transfer to a Solvent in Coordination Polymerization

Low-molecular-weight polystyrene (LMPS) is the precursor of a brominated styrene oligomer that is used for small, precise, thin electrical components and an environmentally benign flame-retardant material. To date, LMPS is usually synthesized via anionic polymerization or radical suspension polymerization. With respect to coordination polymerization, the molecular weight is mainly controlled through chain-transfer reaction between the active species and the chain-transfer agents or monomers. Herein, we report an unprecedented chain transfer to toluene of an extremely high efficiency for styrene coordination polymerization, which is triggered by addition of an organic additive alloxybenzene (AOB) to the scandium catalytic system that gives high-molecular-weight polystyrene with excellent syndiotacticity. The polymerization of styrene catalyzed by a scandium bis­(alkyl) precursor combining [Ph3C]­[B­(C6F5)4] and Al i Bu3 exhibits high activity to give syndiotactic polystyrenes with tunable molecular weights. Interestingly, with the addition of an equivalent AOB to the scandium precursor, the polymerization occurs slowly but quantitatively. It is worth noting that is that the isolated products have very low molecular weights varying in a very narrow range (2.2–5.8 × 103) and are amorphous. End-group analysis suggests the occurrence of strong chain transfer to toluene. The influences of additive structures and polymerization conditions on the chain-transfer reaction are elucidated.