Synthesis of multifunctional dithioesters using tetraphosphorus decasulfide and their behavior as RAFT agents

The reaction of tetraphosphorus decasulfide (P₄S₁₀) with multicarboxylic acids and benzyl thiol afforded multifunctional dithioesters by a simple experimental procedure. The dithioesters were subsequently used as chain transfer agents to grow poly(iert-butylacrylate) and/or polystyrene chains in a controlled fashion by reversible addition-fragmentation chain transfer (RAFT). RAFT polymerizations of styrene were performed thermally at 110°C either in bulk or in toluene solution, while tert-butylacrylate was polymerized at 60°C in toluene in the presence of AIBN as the radical source. The multifunctional RAFT agents provided good control over the molar masses and polydispersities of the polymers formed, even though the presence of some linear dead chains generated by irreversible terminations could not be avoided. The contribution of the latter reactions was enhanced with the increase of viscosity at high conversion and with the "shielding effect" created by the polymeric arms around the RAFT centers of the core. Better control could be achieved when performing RAFT-mediated polymerizations in toluene solution as compared to bulk experiments. This methodology was applied to synthesize not only linear poly(iertbutylacrylate-b-styrene-b-tert-butylacrylate) triblock copolymers, but also three-arm polystyrene stars following an "arm-first" approach.